Sure, but when looking at performance "upgrades" in any speed sport, aero is the thing that bumps you from 99.5% to 99.9%, it is something that can bump up speed a bit when much larger contributions are running consistently as fast as they can. It is absolutely critical at top competition, because everyone else has the body tuned out, it can provide the marginal gains you need to win.

Yes, someone averaging 15mph can go marginally faster with a suit, but they aren't consistent to the point where you can actually look at the suit and notice it making any difference. They may well beat their suit time in jean shorts and a cotton tshirt the next day, simply because that day they got into a better rhythm.