They pretty much look like bald, working-class vulcans to me.
Maybe you should have another look.
Those actors wore shitloads of prosthetics, and not just on their ears.
Mostly for bald caps and scarring, rather than something that distinctly human.
An interesting look, and scaled back from what was planned/thought about, but still clearly in line with TOS. Far more so than the TNG Romulans, actually.