Swerve has to win the belt, imo. You kill him if he doesn't beat Joe and then has to play n°2 babyface while Ospreay goes for the belt at Wembley, he just becomes another guy on the roster and I don't think AEW can afford that.
Strickland winning would feel important. And him main eventing a 50-60k Wembley as champion against a white hot Ospreay would elevate him and solidify him to a point where you can then start putting him in angles and feuds without a belt and still feel big. Swerve vs MJF, Swerve vs Mox, Swerve vs Cole (well, Cole fucking sucks but I'm talking from what the core AEW fanbase seem to perceive as big deals) would all feel much more impactful if Strickland has a 4 month run that culminates in the second biggest show of the year in all of wrestling (after Mania weekend, of course).