I've seen plenty of fans who think Dembele will be better. More think Mbappe is better, give you that, but Barca paid about 160m. on Dembele with addons included, and PSG will pay 180m. for Mbappe.
So, they're both rated ultra high, with not that much between them. Dembele plays for the much bigger club, in the much better league. He has all the tools to become better than Mbappe. Talent wise, they're in the same ball-park as well.
I disagree. Mbappe is a generation player. A phenom.He is on another level.