Sarmad Khoosat is the son of Irfan Khoosat - a veteran "character actor" who has been on PTV (the pak equivalent of Doordarshan) for ages - and now he appears in private productions (after the introduction of private TV channels galore - thanks to Musharraf/Sheikh Rashid - while most politicians opposed such a move - ok, digressing here ..).
Irfan Khoosat is known for playing usually comic and buffoonery type of roles - though not to the extreme of Johnny Level - but he has played Johnny Lever-esque characters - so I would say he is somewhere between classical/dramatic actors and the Johnny Level extreme. Perhaps he is best known for his portrayal of a corrupt police sergeant working under the gaze of an honest police officer - which is an iconic role for Khoosat where he portrays his basic understanding of what he is doing is wrong - but can't help it because of how he has operated in the past.
He is perhaps the male equivalent of the Khirron Kher playing the punjabi mom - but if instead she started playing the punjabi female constable in police stations or something.
EDIT: here is a youtube clip of Irfan Khoosat recreating his role of the police sergeant in a TV show (hosted by Moin Akhter):
http://www.youtube.com/watch?v=CTbig7AgIBM
Legendary Irfan Khoosat (Direct Hawaldar) & Lehri With Moin Akhter Sir In Ptv Awards 1983 Classics
EDIT: here is a youtube clip from the original show "Andhera Ujala" (i.e. darkness/brightness as in despair/brightness type of meaning):
http://www.youtube.com/watch?v=CTbig7AgIBM
Andhera Ujala - Akas Bale Part 1
EDIT: In this drama - in the scene the first police sergeant who speaks was a very good actor in this role - and exactly matches the typical "efficient but slightly corrupt" police sergeant type (if there is such a type!) - while Irfan Khoosat is the buffoonish police guy on the extreme right who is speaking in a buffoonery type of way. He played a character who was often sympathetic with the criminals (or oppressed citizens) - but also accustomed to the usual police corrupt ways. Muhammad Qavi (who is another famous character actor - playing characters like Ghalib etc. - though an older actor played him better and even looked a bit like Ghalib) - in this series Qavi played the part of the honest police official (who is superior officer to the others in the police station).
EDIT: here is a complete episode to give you a flavor for the play:
http://www.youtube.com/watch?v=0IFvMEFhdM8
Andhera Ujala ( Azaab ) Rashid Dar & Younus Javed's Ptv Classic Drama Series.
However, Khoosat would have very rarely been cast in an "intellectual" role - and perhaps that is because of his main body of work - i.e. playing country bumpkin type of roles. But he I think would be very popular in the Punjabi viewing public - especially for that. For other audiences he would always be the "Punjabi" guy in the scene perhaps. I think n later years he has started playing more mainstream roles in urdu plays i.e. playing a non-punjabi character - or playing the educated punjabi character as elder father etc.
In my own opinion (i.e. without knowing anything beyond Khoosat and having seen his son appear occasionally in some TV show or something - his son may have started as an actor possibly ?) - I did not have a high opinion of him.
Now it is possibly that he has emerged as a radically different talent than his father - i.e. the son being the product of education in Lahore (in contrast to if his father was from a more rural background) - and that is perhaps why the son is capable of producing slick plays etc.
However I would suspect (again without knowing anything - and primarily based on bias/intuition whatever - after all intuition is the process of conclusion in the absence of hard facts) - that the primary reason Humsafar was a success - was in the slickness/sensitivity/alertness of the writer - AND the oversight of the women who run Hum TV (since Hum TV is a women-dominated channel - primarily catering to the women audience and with women who were producers at PTV in it's heyday) - and given the photos that were posted showing Momina Duraid (?) or whatever sitting during the shooting of Humsafar etc. - it would make sense that the PRIMARY reason things are slick - is because of the women exercising oversight.
I would suspect that Sarmad Khoosat's role - would be interchangeable (in any case he seems to have an issue with how Fawad Khan was playing the role - so it is possible that Sarmad is more conventional - being informed by the legacy of his father/PTV and punjabi-themed roles - compared to the more off-the-cuff and spontaneous Fawad Khan intent to play his role (I am guessing - since Fawad is a newcomer i.e. is not bringing with him a "legacy" of tradition in acting or whatever - and has a more diverse background - essentially coming into the industry as an outsider - and thus open to doing things differently (and perhaps more novel ways).
Now if Fawad was really going against what the play was standing for - we would see that tension between Momina Duraid and FK etc. being exhibited - which it has not. The problems people mentioned between HumTV and FK etc. seem to be of an economic/agreement type of thing i.e. they wanted FK to be in something else/some movie or whatever - and he was not available - and not of the type which suggest intellectual tension on the set.
EDIT: An interesting point is one mentioned many times here - that the "director" of Humsafar - thought the lead actors had "no chemistry" - but after seeing it later (or after seeing how public was reacting) he commented that they have "amazing chemistry" or whatever - that right there shows that the director is most probably an idiot - i.e. is an uncouth type of person who could not imagine what would be on film when he was filming on set - and he basically wanted them to overact (as his father overacted in punjabi-themed roles) - and if people had listened to Sarmad Khoosat it would have totally destroyed the subtlety that FK was going for (possibly - against completely speculating here). But in any case it says something about the judgement of the director that he said something else while filming - and then completely reversed himself - which if anything suggests that he was someone whose advice SHOULD have been completely ignored while filming (!)
I would suspect that Sarmad Khoosat would have provided the technical part of the process - and may dare to say that he could probably have been replaced by another director (after all he was brought in when someone else went away - from what I recall from some comments on this forum).
In any case Sarmad Khoosat does not seem to ooze "brilliance" - or words of that nature. Maybe he is smart that way - but at least he does not give the vibe of an intelligent thinking or reticent kind of guy - just seems like a goofy type of "average joe" type of fellow (wow - loads of blanket judgemental views based on no facts !!).
In any case - I suspect what made Humsafar/ZGH - were the scripts - the women involved in ensuring it was done right (for women audience - i.e. plays being "intelligent for women" - i.e. the input/overview/supervision of Momina Duraid/Sultana Siddiqui - I don't know the infrastructure of Hum TV - but I suspect is may have a far more women-centric and women-sensitive environment than say some of the the other male-oriented channels) - and lastly the actors - who were chosen to be empathizable (because a good story/movie with actors you don't root for can lose it's steam very quickly - for example since I don't have great opinion of Hritik Roshan/Katrina Kaif - it failed to make me care about what the actors were doing on screen - another example is the Godzilla movie - where I thought the male lead (from Kickass) and his wife were both miscast - and they were not able to carry the movie audience along with them in their plight).
After all - this is why movies pick actors who are "liked" by the audience - because audiences apply their blanket views based on how a person looks - if they look like a kind person - or they look like an asshole etc. If an actor reminds someone of some asshole in high school - they are far less likely to empathize with him and his story in the movie.
Same thing with Humsafar - they were able to get actors - who public thought were innocent enough or believeable in their roles - so some credit to the casting folks (who maybe the same people anyway - this is after all not a big budget hollywood movie).
I would guess that a replacement of the director would have achieved something very similar either way - i.e. Sarmad Khoosat could have been replaced with another.
However I don't have a recollection of whether Sarmad Khoosat has a great body of brilliant/sensitive work or not - but maybe he does ..