Højlund has already been clocked at 35.45 km/h in PL in which he has played less than 800 minutes. You shouldn't really take this "top speed" literally. Dominic Solanke has been clocked at 36.10, but we all know he isn't as quick as Mbappé. Acceleration is very important as well.
Osimhen is dispossessed almost equally as much as Højlund. And just to add to what Højlund does better - statistically - progressive passing, shot-creating actions, take-ons, progressive carries, progressive passes received (hold-up), carries into penalty area, passing distance, passes per 90, pass completion, etc. Osimhen really isn't better when it comes to ball retention, carrying or dribbling.