Konstantin counter is Harec. That is why I always try to keep Harec and Konstantin in my team whatever map I go but the third one (The second from Alien), Snipers dont do that well here IMO.
You can play against him, and he isn't the antagonist against who I had more problems, he is the one that is the easiest to do a decent-good job. His slowliness is his biggest weakness and why I dont put him as the hardest antagonist. Even if I lost against a lot of Konstantin's antagonists.
He has an incredible dmg and good defense abilities, so maybe he needs a nerf, but if he recieve a nerf too big I think he will be useless. There are characters that have a damage close to Konstantin, so you can't put him behind that ones.
Maybe same damage mid range but less dmg on close range. That would keep him playing in mid-large range as he is designed (I think?) but he wouldn't be that lethal in close range. Where Lycus and Alicia should be the best IMO.
BTW, I hate playing as konstantin and Harec
Edit: I don't put Konstantin as the hardest one because his slowliness dont let him play as aggressive as others chars. I save the first spot for antagonists with high mobility chars that play really aggressive and know how to play well.