This isn't a valid comparison. Haaland is now tearing it up in the PL, so people's opinion are going to be raised, but the PL is overrated and Mbappe would be just as devastating in that City team, but they're different players. Mbappe's more dangerous in a bigger part of the pitch, can create his own goal when the team is out of ideas, is a much better creator, and can finish at an elite level. Haaland's more dangerous in the box, his finishing is beyond elite, I don't know what the term is for it but near-perfect, is physically superior to almost anybody, and is as fast as a guy his size can get. They each can score goals the other cannot, that's why I think the comparison is silly, even though it's inevitable as they're the top two talents of their generation. The main differentiating factor between the two where I prefer Mbappe is the quick feet that he has, he makes it very difficult for defenders to deal with, whereas Haaland, silly to say right now but I still believe, is easier to contain in 1v1 or 1v2 with defenders.
In a team like City, I'd prefer Haaland over Mbappe now that I've seen it with my own eyes. For most other teams, I'd prefer Mbappe over Haaland. Mbappe's been around for longer, been through a ton of media scrutiny that Haaland's yet to experience, and has come out continuing to get better. His numbers across any competitions are ridiculous and well-balanced between goals and assists. Last season was about as good as an individual can do in such a dysfunctional side, and he tormented Real Madrid in a way I don't see Haaland capable of in that PSG side.
The media loves to bring a guy up and then tear him down, Mbappe was the golden boy, now he's persona non grata, and that will likely happen to Haaland too over the course of his career as the spotlight gets bigger. But it's absolutely ridiculous to think Mbappe's mentality is any weaker, he's been through far more and it hasn't stopped him.
It's funny though, just when we're getting wrapped up with the nauseating CR7 vs Messi debate, we will now get to enjoy this for the next ten years.