You biased? Rashford biggest weakness as a striker is to be at the right place at the right time. He is very versatile in his general play when he is on form. He can hit long passes, good vision. He used to be more of a playmaking winger as a youth, before becoming more of a striker/forward as he got bigger. He has a lot of stuff in his locker that isn't coming out on a consistent basis yet. Mbappe is definitly further along in his development and has found himself while Rashford is still struggling for consistency and seems to have some issues with the mental aspect if you ask me. If he can establish himself at that top level, it is not much between them in talent, imo. As you said different players, and both currently very young and both still with a lot to learn. I feel pretty certain Mbappe will at least continue on this path while Rashford I'm more uncertain about, but you can't rule him out on the basis of lack of consistency in such a young age, just because Mbappe seems to be ridiculously consistent at such an age.
Anyways, don't see the point in comparing them. But of course you probably haven't seen the best and worst of Rashford as I have, and I have only seen the good from Mbappe. Except yesterday, he wasn't all that, where as I have seen Rashford put in a much better performance in a similar setup as a striker, with no right wing to help him etc... But with young players it is all about form and finding that consistency. Some games Rashford is showing a lot, and I wouldn't put many above him in those games, but then you get disappointed next game when he doesn't show up, like against PSG. I expected him to maybe run at your defence and get them to foul him, well they did and should have seen red, maybe he could have effected the game more after things opened up a bit, like Mbappe did. I wouldn't have ruled it out, but he certainly didn't have his big boy pants on that game.