The reason why GT Sport is going to have such a low car count, is because PDI is a SMALL studio. PDI only has more than 200 employees, and that is a low number for a gaming studio! Especially for one that is responsible for Sony's most successful franchise! In comparison, Turn 10 has over 300 employees, and they also do something PD doesn't: outsourcing. And because of that, Forza Motorsport 7 will have over 700 cars compared to GT Sport's meagre 150 (or at least, that's the official number, GT Sport could have more cars than that). Now it is true that PD's 150 cars are the most detailed in the racing game industry, with the interiors and exteriors (most likely) having higher polygon counts and better textures. But just like
@SlipZtrEm pointed out, these car models don't have any under-hood modelling. Or perhaps there is, and PD is about to unveil a damage model which includes hoods/bonnets flying off the cars. But I'm gonna assume there isn't, because nothing of that sort has been confirmed (yet).
GT will still have that car collecting feel for a part, but it won't be the same as it was before (obviously). There won't be any tuning as far as we know. There won't be any customisation apart from the Livery Editor.
Does that bother me? Yeah, a little bit. Will it stop me from buying GT Sport? No! I've always enjoyed GT games, and this one will be a good one for me! I like the idea of Sport mode, and I've always wanted a more competitive GT!
But I also know this GT won't satisfy everyone. Not everyone wants competitive racing, which I completely understand. Some people, including
@Scaff, prefer a serious simulation instead of a more entry-level sim like GT Sport will be. PD can't satisfy everyone.
But what Kaz needs to do, is hire dozens employees for PDI, especially car- and track modellers, as they are becoming too slow to keep up with the competition. :/