However, A sidereal of essence 5+ is limited in what charms they can learn; Solars, Lunars, hell even Terrestrials that live that long will be learning high essence charms in what ever ability they are interested in. Sidereals will be learning MA charms if they want anything with an essence requirement over about 4.
I like to look at it this way; Every dawn caste solar has MA as a caste ability. So that's  roughly going to be 30 of the 150 solar shards still manifesting as solars. of the 120 non dawn solars, if you assume it equally likely that any given out of caste ability is favored (Admitably a shaky assumption, but lets go with it for now), that's roughly another 30 solars. So, even taking into account that abilities that let you not get your head ripped off are probably more likely to be a favoured ability than, say, sail, I'd rate it as unlikely that more than half of all solars have MA as a caste or favored ability.
I'm not going to address solars who don't have MA as caste or favored going to the effort of learning an entire Celestial style and then embarking on the task of learning a Sidereal one instead of learning high essence charms in the abilities that they have a natural competence in - I'm sure it could happen in interesting situations (and I do like interesting situations), but isn't relevant to the sort of statistical view I'm going for here.
Now, of the 120 Siderials, obviously even less of them are going to have MA as caste or auspicious abilities. However, an essence 5+ Sidereal isn't faced with the choice of learning essence 5+ charms in a caste or auspicious ability or learning essence 5+ charms in an out of caste and non-auspicious ability: Sidereals learn MA charms at that level or nothing. If they're not Endings or don't have MA as an auspicious ability, tough luck - they just have to pay more xp or not learn powerful charms.
I like to look at it this way; Every dawn caste solar has MA as a caste ability. So that's  roughly going to be 30 of the 150 solar shards still manifesting as solars. of the 120 non dawn solars, if you assume it equally likely that any given out of caste ability is favored (Admitably a shaky assumption, but lets go with it for now), that's roughly another 30 solars. So, even taking into account that abilities that let you not get your head ripped off are probably more likely to be a favoured ability than, say, sail, I'd rate it as unlikely that more than half of all solars have MA as a caste or favored ability.
I'm not going to address solars who don't have MA as caste or favored going to the effort of learning an entire Celestial style and then embarking on the task of learning a Sidereal one instead of learning high essence charms in the abilities that they have a natural competence in - I'm sure it could happen in interesting situations (and I do like interesting situations), but isn't relevant to the sort of statistical view I'm going for here.
Now, of the 120 Siderials, obviously even less of them are going to have MA as caste or auspicious abilities. However, an essence 5+ Sidereal isn't faced with the choice of learning essence 5+ charms in a caste or auspicious ability or learning essence 5+ charms in an out of caste and non-auspicious ability: Sidereals learn MA charms at that level or nothing. If they're not Endings or don't have MA as an auspicious ability, tough luck - they just have to pay more xp or not learn powerful charms.