They're both doing excellently.
We're harsh on our young players as is the case at a top club. But I think fans there should be a greater sense of excitement and contenment regarding these two than there is. For me, we've got two young footballers at the club as good (or thereabouts) as any in the country. The difference you see with City's youngsters is that they play in a better team and get more 'service' as opposed to what happens at United where our two have to create much of the openings on their own. Not to mention the general overload their team creates which means their players are always on the front foot and have far far lesser to do defensively.
For me, Martial is one who can genuinely be one of the best around. His all round is already at a superb level. Barring the odd bad game, I think he's one of our best players most games. His touch, intelligence, dribbling, finishing, athleticism etc. ensure that. I don't think he needs a huge improvement to reach the bracket the OP mentions. Rashford has a lower cieling from what I see but he can still be a top player (a level or two below elite). He is intelligent, scores goals, has decent delivery, good athleticism, boat loads of pace etc. Just because he doesn't have those 'elite' natural qualities that Martial does, that doesn't mean he can't be a great player in his own right.
These two are the future for me. And we have to get them to their potential as much as anything. They're assets of ours and us being successful will depend on them being as good as they can (as well as a lot of other factors of course).