900w ceiling would be a bit frustrating even if it's a theoretical thing. Meaning maybe in real life a 1000w sprint is your max, it's still higher than 900w. I can sustain, at least for 5s (that's what Zwift displays when ending a ride) 1000-1100w semi regularly, so having a "no cap" SRM is nice. If that was capped at 900w that would be disappointing.

The jump is worth something. If you can get a good jump in a Zwift sprint, with the ~1 second built in lag, that's a tremendous advantage in a sprint. Or, in my case, a huge deficit to make up if someone I'm following goes a bit early (I don't race so I'm just sprinting for time/jersey). My sustained sprint probably isn't 900w for more than 8 or 10 seconds on the trainer but it's certainly higher than that for 5 seconds.