Hi,
I was thinking about adding a uncapper, but I'm thinking it is going to make my character a really powerful entity. I wonder what's your idea. Will it turn out that I could kill all people in just two hits for example, just by having 200 in the 'blade' skill?

Well, I usually use mods that add more powerful and more numerous enemies. So a blade skill at 200 feels very balanced to me.

Even without creature or overhaul mods I think a 200 Blade skill would still be okay. In vanilla, hgher-level enemies mostly tend to be scaled. If you continue to level your character up but don't have some way to increase the damage of your weapon you are going to be at a disadvantage, in terms of damage.

So, in short, I think uncappers do not unbalance the game.