Let’s see if this is real, or if it’s only a matter of comparing a level 10 fighter with a level 3 monster.
So, let’s look at, say, a Fire Giant (CR 10, just like a Human Fighter 10)
The above-mentioned fighter is attacking full out with PA, for a total of…
Greatsword +12/+7 (2D6+30) [Average 37]
His AC should be around (Armor 10, Dex 1, Natural 2, Deflection 2) = 25
Hp will be something like 60+(10*Con) so maybe 90 Hp
The giant, on the other hand…
Melee +20 / +15 / +10 (2D8+15) [Average 24]
(Power attacking for 8) Melee +12 / +7 / +2 (2D8+30) [Average 39]
Ac is 21
Hp are 142
So as it is, the giant has 50 more HP, an extra attack, and reach (plus other stuff like fire immunity). The fighter will have his hands very full! Of course, it gets MUCH worse if you figure the Fire Giant is an NPC and gets gear. Then it’s bye bye fighter!
Long story short, power attack is not broken. Or if it IS broken, it’s not because a level 10 fighter can kill a CR 3 monster pretty often.
-Tatsu