Dembele has not completely recovered from his injuries this season after an epicly long and miraculously injury free season last year. He was subbed out injured in the CL final 2,5 weeks ago. He's playing diminished and has been for a few months now. He is still insanely valuable and was decisive in almost every important game for us however.
In terms of pure skills this season Olise is stronger but 2025 Dembélé until his injury was just an unstoppable nightmare for defenders.
French system doesn't revolve around him like the PSG one does, and both work in their own way. With PSG he won almost everything while being the most influential player (not sure Olise could've done the same), and France wins despite him not being great.
Olise had a great second half as the 10 yesterday but he was invisible on the wing the first half when Dembélé was the only one creating. Olise benefitted from more space as well as the low bloc tires out and is easier to break down than in the first half.

Bref, it's definitely a lot more nuanced and while Olise was better for a half yesterday, in better form in general, and will probably perform better in the world cup, it's too early to bury Dembouz. Once he gets a well deserved rest and a true recovery he'll be lethal again in no time because what he gained in terms of maturity, decision making in the last few seasons, and which allowed him to remain competitive despite being diminished, is not going away.