No it is more than just cosmetics. The store also contains boosters and ghosts which affect (albeit to a small degree) gameplay itself.
The main issue however is that there is so much within the Eververse store that should have been rewards from simply playing the damn game. Where for example are the ghosts, ships, and sparrows that used to drop from raids? Oh thats right, money...
In a loot based non F2P game which is distinctly lacking in end game relevant loot, having a significant portion of items (that could otherwise BE endgame collectables) being stuck behind a paywall is a ******* joke.
D2 is an utter mess right now (a perfect example being the writers on CoO seemingly forgetting half of the lore that already existed) and Bungie have no goodwill left anymore to act like they can simply ignore the problem.