It doesn't, but as long as Mbappe plays for PSG in Ligue 1 as his dayjob, we'll never know. Haaland is the best goalscorer in the world though. I doubt any team having those two would bench one and play the other, they'd find a way to get the best out of both if they had any sense.
They are completely different playertypes, so comparing them really is a silly exercise. Some likes the dribbler/playmaker, some likes the goalscorer, it'll allways be subjective in the end. Both needs good teams around them to win trophies.
Statswise they both stand out: Haaland as the goalscorer and Mbappe as the overall contributer.
Right now Haaland is pulverizing every record in the toughest league in the world in his debut season, while Mbappe is still playing it safe at PSG, so at clublevel there is no doubt who is pulling up the biggest trees at the moment.
I'm 6'4'' and have played as a #9 all my career (lower levels) myself, so there's no hiding that I'm biased towards the pure specialist, with the monster physique. The combination of movement, positional awareness, pace, strenght and finishing he has is unique and I've never seen a better pure goalscorer. Not many goal records will survive the Goal Yeti if he stays away from serious injury. His goalscoring record is so ridiculously much better than anyone else's in the top 5 leagues at his age the last 60 years that it's hard to grasp.
Others like the more rounded type of player that gets more involved better, and that's fine. I get more exited by watching Haaland make grown men look like boys in and around the box and score with 30+% of his shots than watching Mbabbe dribble/or sprint past defenders which he succeeds at 34% of the time he tries. I think defenders fear Haaland more than they fear Mbappe.
I think chance creation/playmaking is the most difficult discipline in football which is why there are no pure goal scorers or defenders considered among the usual suspects in greatest of all time discussions. Haaland is obviously a freak in terms of goal scoring but for me, a player that reliant on service can't really be considered the best in the world. Mbappe is also very focused on goals, just not as much as Haaland. I enjoy watching both and hope they break every record they can but I think it is a bit annoying that people focus on goal stats that much. Generally I think this generation will be much more even in terms of top players. Nobody will stand out by the margins Messi and Cristiano used to. Here's hoping that players such as Gavi, Wirtz, Pedri, Musiala, etc. fulfill their potential because those type of players are much more involved and on their day are capable of having 20+ great plays in a game while Haaland and to a lesser extent Mbappe are often invisible until they score, even if they do it twice or thrice.