>This is misleading, because it assumes that i/I naturally represent one vowel, which is just not the case.

It does in literally any language using a latin alphabet other than Turkish.

All other Turkic languages also copied this for their Latin script: https://en.wikipedia.org/wiki/Dotless_I

This may be correct, I'd have to do a 'real' search, which I'm too lazy to do, lol sorry. However there are definitely other (non-latin) scripts that have either i or I, but for which i/I is not a correct pair. For example, greek has ι/Ι too.