I agree that none of them come with SUV like profile tires as it's more of a crossover.
But, I wouldn't consider the 19" tire as being low profile.
If my calculations are correct the side walls are as follows
19 -> 4.5" of sidewall
20 -> 4" of sidewall
21 -> 3.5" of sidewall.
As an owner of the M3P+ (which is now the standard performance model) I think I made a mistake in not getting the Stealth version due the ramifications of the larger brakes.
That I have to basically have a second sets of wheels/tires.
But, at least with the M3P it makes sense as it's a sports sedan, and not a cross over. On the Y I simply don't see the 21" tires making a whole lot of sense due to the summer restriction and the small sidewall.