If that's the case, it isnt really helpfull to max out the one handed weapon tree. The top 3 skills are all for power attacks..(different ones)
Am I right?
I'd say yes... for the most part. When using two weapons you can still just swing one at a time which allows you to take advantage of the extra/bonuses to power attacks with one-handed weapons. If you use the dual wield power attack you just get the 'flurry' animation.
So I'd say they are still very useful even if you only get one dual wield power attack.