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.
I never brought up cross-play for either game. The way SFIV added stuff (releasing a separate Super SFIV and then a separate Ultra SFIV) or MvC3 (and then releasing a separate MvC3 Ultimate) was completely different from how KI did it (one release, 3 seasons). Even if we don't agree on that, those games were from the gen before. We're talking about defining THIS gen!
Also, you mention that other genres did it before, and were successful, unlike KI. First of all, we're discussing fighting games (I believe KI was the first this gen to do it the way they did). Second, I already discussed how KI was already facing an uphill battle releasing on Xbox One, but also not having the brand awareness of SF, Tekken, MK, Smash, etc. And then having to go against SFV...so yeah, KI had a lot to overcome and didn't quite get there.
HOWEVER, SFV, Tekken 7, Smash U, MK11...they ALL adopted the "Season" model from KI which proved to be very successful in increasing revenue and sustainability for each of those franchises! KI says you're welcome!