I think most people...umm, don't know how to put this because I don't want to say anything about tastes...but let's just say most people who have seen his movies would and
do rate him as one of the best directors of today. But those whom his movies don't reach, i.e. people who have seen pretty much none of the stuff you've mentioned in your post? Unfortunately, those are the masses. To be significantly rated as a big/best director, you need to have reach...that's how people start talking about you, expecting your movies, considering you as popular. Same is the case with lots of actors...they're heads and shoulders above others, but don't have similar viewership to gain appreciation and thus popularity while many average or non-actors get regularly mentioned or hailed by the masses.
For Dibakar though, I will say that many times, I have seen people on this forum wish for their favourites to work with him...which says enough. Him, Vishal Bhardwaj, and Motwane are some of the directors regularly mentioned in hopes of seeing 'quality work' and 'versatility' in actor portfolios.
As for why SLB, KJo, Imtiaz get more mileage than their work actually deserves...easy enough, no...people like looking at pretty things...wall hangings, curtains, clothes...😆 People like seeing flossy, glitzy, glamorous stuff. And Imtiaz...pretty sure he's just hanging around and lasting on the basis of a past, one-time glory.