Out of the 80 heroes that are currently ported, only 2 are pretty much never used in competitive play. Incidentally, they're both pretty strong in low-mid level pubs. In competitive play, some heroes are banned rather often (but not always, which is what would happen to any actually overpowered hero) and there's a pool of a ~dozen heroes or so that are banned and picked in many games, but usually because they either are heroes that fit into the current meta well or because they're really versatile in terms of what role they can fill and where they can be laned, which means that teams who pick them up in the first round of picks don't give away much of their overall strategy to the other team before the second round of picks & bans.
Usually heroes that fill the relatively same role have very different strenghts & weaknesses, so you can't flat out say 'X is better than Y.'
And people give too much value to hero counters, KotL is far from being the only way to stop a Chen. I don't see any of the heroes that are missing alone having a massive impact in the game, not in my ordinary pub game or any pro game I watch (except Techies, that will ruin many of my games.)