Sean o malley is the better striker, certainly more accurate but tj dillashaws activity and cardio could for sure be a problem just based on the way suga fights. Tjs activity is legendary, for many reasons, and poses a serious problem for someone like sean who can take rounds off looking for big shots. Tjs fight IQ is another problem for sean, his ability to adjust mid fight and recognize openings are excellent. Against garbrandt he was having trouble against him early and made literally two adjustments and proceeded to finish him within the next couple of minutes.
Tj is hittable though, and doesn't have some legendary chin, also his footwork advantage he held over alot of fighters wouldn't be there against O malley and the fights we have seen where fighters can match his footwork gave him serious trouble, particularly Dominic Cruz.
The more I think about this matchup it's actually a super bad ass fight. I'd have love to have seen that in their primes. I probably gotta lean TJ by decision, but sean could for sure end up busting his face up with big shots.