I think I would completely agree for you if it were a definition and not a type annotation!

That is, "x: 5" instead of "x = 5" (or "x ← 5", &c) looks fine to my eyes. And of course, that's how values for the members of a struct are in fact defined in many languages (such as Rust).

I suppose the underlying point is that has-type is a relation, not a definition. Asymmetrical space around a binary relation violates (my) experience, but it's also a bit confusing to use the same syntax for definition and type annotation.