It is, of course, a minor harm, like all stylistic choices in a language. However, all of these minor harms add up, so what you don't find bothersome, or even prefer, can impact those both new and old. So please don't dismiss the concerns of others because you don't see it. Like you said, this is largely a stylistic issue, and brings with it quite subjective opinions. That those opinions differ from yours doesn't mean they don't exist (or that's there's "little evidence").
Sure, in the same way that requiring paired parenthesis, decimal points, or semicolons impose a stylistic preference. Many languages get away without those, or mixing them, any number of things. So I suppose I should say this allows a stylistic preference that has negative consequences for the readability of the code, and pushes Swift further down that path when some in the community already find Swift increasingly unreadable (if for other reasons). But given the proposal directly cites the preference of various repos, it can hardly be said that there's no preferencing going on, as there's an evolution proposal up for review.
In some ways even allowing the choice is a minor harm, as it forces the community to create tooling and form opinions one way or the other. This would be less relevant if Swift had a built-in formatter or linter like Go, but so far it doesn't (I think I read that swift-format now ships with the Swift 6 toolchains though?).