Its not an explanation for why the game is janky. Its a rebuttal to the comment that HS(card games in general, really) is bare bones or should be trivial to run well. Almost certainly they could fix the issue with background thread loading and some UI tweaks if they wanted to. That said, the issue is most likely that they're simply loading texture data from disk on the main thread. This is the default Unity behavior with asset loads and it's not really possible to hit their RAM quotas if they load every card. A subset of cards reveals information.
Maybe more clearly, whenever you enter a game there's a loading spinner that freezes for several seconds even on the very highest end desktops; you'd think for a game whose main graphics concern is exactly "image asset streaming from disk", they have wouldn't need to hard-freeze the menu UI to do the loading.