I think there is a qualitative difference between affecting an enchantment, something that is already shaped wind and affecting the world. Also it should be noted that Mandred had a mother who is an anointed priest, not that his father knew that, and he could be discretely assigned perpetuals to make sure he did not reach out without meaning to and that his parents would be alerted the moment he did. The fate of random farmer's children out in the boonies and the Emperor's son should not be compared, not least because the former got found out way earlier than any reasonable standard
Well if we're talking about statistics
Statistically only 1 in 3 people who have the ability to do magic, or "channel", end up in the Colleges.
The remaining 2/3rds either never touch magic despite having the ability to use it, touch it once and then slam a mental block over it, or become divine casters
It's not known how those three groups divide the remaining magic capable populus amongst themselves, but I personally think it makes sense that divine casters would be the rarest
Unlike the Colleges there is no legal funnel directing them to the priesthood, nor are there any noted programs scouring the population specifically for recruits like how the Light College picks through orphanages
If the Colleges actively take measures to funnel in people with magic and still only end up with 1/3rd of them, then the various Cults would logically have even less than that
Particularly because the Cults tend to get testy about the idea that Miracle wielders are in any way related to Magickers, especially Sigmarites and Ulricans
Regardless, the majority of potential Wizards do not become Wizards
And a very significant portion, if not the outright majority, either never channel despite having the ability to or channel once and then don't do it again
Which doesn't fit with your assertion that anyone with the ability to channel is going to be constantly shifting the winds around subconsciously and presenting a constant danger to themselves or others
And that's not just Mathilde talking, that's Boney communicating world building and back of envelope maths through her
"So, we estimate one in a hundred people have Magesight. About one in ten of those will have some ability to actually use magic - so, one person in a thousand. That's any ability at all. A lot of people will never actually use it, sometimes the ability lies dormant their entire lives, sometimes they have one bad experience and consciously or subconsciously slam the door on it. A lot of people react by turning to the priesthood. Those left over - about a third of those one in a thousand - end up at the Colleges.
- Canonical note: The numbers Mathilde gave to Wilhelmina are my own back-of-the-envelope maths. Canonical population numbers for the Empire are absurdly small with some provinces having as few as ten thousand citizens, so I've given them the 15 million of the mid-1600's Holy Roman Empire and doubled that for magical recruitment purposes to account for Tilea, Estalia, the Border Princes, and smuggled male magic-users from Bretonnia and Kislev. Something I've seen said in the fandom a few times is that 'one in a thousand can see magic, one in a thousand of those can use magic', and I've got no idea where that comes from and suspect it's a misremembering of something from 40k about psykers. 2e Realms of Sorcery outright says 'the most learned agree that perhaps one child in a thousand has the potential to become a spellcaster.'
Note: This is explicitly separate from the group of people who go to the Colleges and are given magic dampeners, Mathilde includes that into the group of people who end up at that Colleges
As for whether someone can regularly touch magic subconsciously in the manner of Someone Who Is Better at the Local Superstition
That's a bit fuzzier but Mathilde does mention Minor Talents. Magickers who can only do one specific thing
From there, we shave away even more. There's Minor Talents - people who can only do one thing or a narrow range of things with magic. Clairvoyants, telekinetics, weather-seers, whatever.
Which implies that you could meet Mystic Margaret, the Seer who really can actually read your tarot to tell you what stocks you ought to invest in tomorrow for only 2 Shillings