It's not good use that excuse, as recent past gens showed us that they won't change their tradition-like barren Post-Game. Having 400 less pokémon is indeed less content but not significantly less when it comes to the playthrough, as transferring contributes near to nothing bar showing off, rushing the game or using them for competitive means.
No. Like the last 2 Generations. BW2 has a great Post-Game, the best of the franchise in fact alongside HG/SS, and it's V Generation. So in those terms (generations), V Gen has Post-Game, something Generations VI and VII lack no matter what version you choose.
As for the rest of your comment, I've addressed it earlier in another post, so I'll not repeat myself. Yes, transferring contributes to everything Pokémon stands for, including competitive purposes and gameplay-related purposes of all kind, be it collecting, sharing, battling, breeding or enjoying variety, which ultimately aims for quality content that affects playability.
It's so obvious that I'll not discuss this matter.
My assessment of value will be based on replay value- how many times can I replay it and have a fresh and unique experience. The wild area alone (and info that you can go anywhere in it, but not catch too powerful Pokémon) heavily hints towards a more non-linear and varied play through experience. If the game delivers on this, I’ll gladly say it was worth (temporarily) losing 400 mons I wouldn’t have ever used in the game anyways (not meaningful content to me).
Basically, post game isn’t my priority, main game variety is.
There are lots of genres about replay value. Roguelikes and Arcades are all about replayability. Pokémon is more about adding and collecting.
Second, almost every modern Pokémon game offers great replayability. You can play V or VI Gen with a lot of team combinations. But you don't even know the Pokémon distribution on this editions. You don't even know, at this point, if the Pokémon distribution of SSh surpasses the variety of Pokémon you can encounter on a determined route. You just know that there's a thing called Wild Area where you can see Pokémon walking. That's all.
You were unable to provide even a list of those "great things that justified erasing hundreds of Pokémon", so at this point, with the informatin we all have, all of your arguments are more about "what you want this Pokémon versions to be" than what they really are. It's fine, but it's wrong. I also like main game variety, both terms are not intended to be exclusive, in fact a good game design should be able to provide main game variety and post-game quality content. The rest is all about wish-lists used as facts and complacence.