as far as padding, margins, alignment, colors, weight, gestalt, overall
design, typography, etc...those decisions should be made by a designer.
I cannot at all agree with you on this point. These are decisions that need to be taken in a user sensitive environment since they can harm eligbility in ways that can affect the UX enormously. Of course, this also depends on how you define "designer", whether it's defined as a graphic designer, UX Designer or some other kind of UI designer.