He is far more popular than his actual ability deserves, but that's because of the great moves he's done off the field. He's twice as good as the doubters think but half as good as his fans think he is. He's a star player, and his numbers show that despite his difficulties and whatever lying health issues he has, but I don't think he has the superstar talent in him though. Is he a starter for England? If he is, I don't think it will be for long, because there's just superior talents in Foden, Grealish, and Sancho and he's not really shown enough to be trusted up front.
What I disagree with is those thinking he's reached his ceiling because he has something like 300 professional games. You can always add more to your game, and he's shown consistency in the past two seasons as far as the numbers go. That's not easy and demands some appreciation. I look at a guy like Mbappe, not to compare the two (because that's already been done here), but very similar in just how many games they've played already for such a young age, and I see improvements in Mbappe when people were saying he was already at his ceiling at feckin' 18 years old playing for Monaco. I think Rashford's maybe hit a road bump due to health or whatever it is, but I expect him to continue to improve and add more consistency to his game with some wrinkles along the way. The problem he's going to have is that there are other England internationals that are improving just as well if not quicker due to being more talented. I think he will always have a starting spot at United (at least while Ole is there), but for England it's possible he is going to struggle soon to get on the field.