Most abilities are capped, but not all. The one that comes to mind is engineers' OH time where, quite simply, "more is better".
Well, if super elite acc gunners have 15 acc and 10 rel bases (is that really the case?), I'd agree with your statement (apart from the possibility of classing them UK reload gunners). "Normal" elite gunners (13/11) in that case are better than those. Super elite reload gunners are well worth it (if they have bases of 10 acc / 15 rel?). To top it off, they also have base 10 repair, which is nice.