Well, yes, I would think a bald head is easier to rectify - should you feel it needs rectifying - than a small penis.
FTR, I don’t necessarily think either needs rectifying.
Only time a guy being bald ever really bothered me, and it wasn’t a dating-type situation anyway, was a few years back at a minor league hockey game. I thought one of the players on the ice was really cute, and according to the stat sheet he was about 24 or so, so I was just really surprised when he took his helmet off and was almost a cue-ball. After the initial “whoa!,” I still thought he was cute. My best friend has a thing for “tall, good-looking black men with shaved heads.” She swooned when Montel Williams was a speaker at her college graduation. (My only question was, what’s wrong with tall, good-looking black men with hair?) FWIW, we’re both white, and as far as I can remember have never discussed what sort of hair we like on white men. I have another friend who thinks Mark Messier is pretty much the hottest guy on the planet. I tend to usually date younger men so I don’t run into the question as much, but it would definitely be more about the guy than about his hair - if he was honestly going bald, I don’t think it’d bother me, but a combover or bad toupee would definitely make me run in the other direction.
In fact, I can only think of two examples of anti-bald prejudice, and neither of them come from women. One is this article. The other is, a couple of years ago Barry Manilow played at the arena where I work part-time, and I heard that he had specifically requested that there not be any bald personnel assigned to the area in front of the stage. He didn’t want the bright lights reflecting off their heads in his eyes.