Few years back casting teams, producers, creatives, some times even channel people were so closely involved in auditioning/filtering various actors & actresses profiles for new daily fiction soaps and it was very time consuming tedious exercise. Seems screen tests/mock tests/look tests were done not just for solo acts, but also for couple acts before finalizing roles vis a vis leads. 👍🏼
The maximum quality of leads we have witnessed on TV screens even upto year 2016 were hence remarkably remembered, mainly for romantic couples chemistry also because of well written character traits with actors/actresses doing some justice with performances. 👏 But quality of leads, characterizations, acting & selections for TV daily soaps has deteriorated since then. 
Now also casting isn't an easy process, but those in selection panel need to have proper judgement for concept & role, plus understand importance of screen presence, leads chemistry with an eye to detail when they finalize people for romantic or married couples, ofcourse in tune with their budgets. This is where there is a gap visible. 😒
Many viewers criticize Balaji TV soaps writings, twists, copy pasted regressive ideas, crappy dragging's, cringe plots, crime loads, nonsense leaps etc. but till year 2016 most of their onscreen TV leads chemistry & casting were still appropriate.😛 Ekta was known to be tough, not easily satisfied & closely involved even in finalizing nuances/styling's of leads. We used to read about her replacing leads even after 1 or 2 months into launch of new soaps if they lacked acting, chemistry or screen presence. But its no longer the case.
E.g. Look at recent Bhagyalakshmi, Parineetii, Dharampatnii leads castings
Here LSD producer Prateek claimed they have auditioned around 120-130 people for RM, he said the same for his new show Rabb too. With initial promos/clips itself most regular fiction TV watchers can make out, casting gone wrong case for these two serials. so what auditioning actually means then?
With RM atleast Shabir & Reeza saved in retaining certain section of viewers in the initial months. But in Rabb typically all three main leads casting & characters have gone wrong with confused plus crime driven execution of bigamy religious concept, they supposedly planned.