Yes, it was originally on XBO but it wasn't the only place to play it. It was available on PC too, so the XBO installbase wasn't that important. In addition to that, what I meant with the PC version and featuring crossplay was already a thing on SFV previous to KI so SFV didn't implement it as an influence of KI.
Many games in the PS3/360 generation like the SFIV series already had post launch content like mechanics, game modes, characters, stages and so on, KI wan't the first one. Same goes with the in-game currency for unlockables goes even beyond that generation, was implemented in games like Marvel vs Capcom.
To increase the volume of post launch content and features and market it as seasons is one of the key parts of GaaS, and like many other things from their GaaS approach they got it from previous GaaS from many other genres in mobile or PC that -unlike KI- were a huge success.
Yes, I mention previous gen influences beacause you talk as if games from previous generations didn't exist and didn't influence the games of this generation.
KI didn't define and wasn't an important influence this generation or previous ones because -even if good- it never has been a top game.