As long as ESPN+ keeps UFC, they'll be fine (especially since ESPN+ is more $ per month than Peacock currently). I also don't see NBC Sports as big of a get for Peacock as much as EPL is, which was already being shown on there. NBC only had EPL and NHL and NHL is a pretty niche sport these days. The Olympics will be big for them, but i'd say that that's a short term gain for them as they're likely to gain a lot in a short amount of time... and then the paying customers from that time will all drop as soon as the olympics are over. It's like dropping WW84 on HBO Max. People only signed up for one reason and then they're gonna leave.
What would TRULY be big imo is if, once the NFL contracts are renegotiated following the 2022 season, will NBC try and stipulate that the Super Bowl be on Peacock? Will ABC/ESPN try and stipulate that they get a Super Bowl and have it on ESPN+? That could truly change everything going forward.