Hm, sneak at 5 is basically the highest you can go, isn't it?
I'd expect it to be somewhat powerful, but I guess that some high-level chars might get better chances to spot sneaking chars even with sneaking 5.
The discussion is a bit strange however, I'll never understand the argument "skill x is so strong you absolutely need it on EVERY CHARACTER. Now that I have it on EVERY CHARACTER, the game is too easy. BUHUUU, fix it, it's broken."
Agreed. You ramp up your character to be all powerful, and then complain that they are 'all powerful.' Be careful what you wish for, as you just might get it!
Having said this, there is no question that the AI needs some tweaking to be more aggressive, and bosses need to be more 'boss' like to ensure that end game is not a complete walk in the park, especially in hard mode.