Yep, I think 90Hz will provide the greatest experience while still delivering amazing battery life.This is what I thought about too. 60hz on an iPhone is so much more smooth than 60hz on Android so I wouldn't be surprised if Apple decides to go with 90hz. It'll probably be no difference than the 120hz on my S21U.
Apple needs to further separate the Pro model iPhones from the standard iPhones so I think the next release we should see 90Hz Pro models wile the standard ones remain at 60Hz, would make the most sense.