while it may be true that him never fighting a girl may be a permanent flaw, there is still a very improbable chance that this may change. people/characters change overtime and it's already been established how slowly some things can occur in HSDK. this is probably a bit of a bad example, but take Saiga. guy started out like a damn nice guy, much like Kenichi being a bit of a pacifist apparently, but after many battles his mindset changed and now he's seemingly the main antagonist.
and while he does have some very impressive resilency, his opponents are increasingly stronger with time, to a point where I'm honestly impressed he hasn't died yet. seriously, he's trying to fight Ogata. if it wasn't for the fact that he's the main character along with Ogata holding back due to him finding Kenichi interesting, Kenichi would have been dead.
and I don't think he's saying that he likes Kenichi more than the others or anything, he's just saying that Kenichi is one of his fav characters. I too can't deny that other shonen heroes are selfish in their own ways while being incredibly likeable (seriously, Ichigo and Naruto are two of my fav shonen characters), he's just pointing out that the desire to kill/annihilate others can both be a flaw and selfish.