And the fact is, Power Strikes gives you greater overall chi generation than Ascension, up until the point at which you have 9787 haste (Venyasure did the calculations over at EJ, but I can't post links), assuming expertise at 7.5%. (It's 9015 haste if you are at 15% expertise.)
Ascension gets you to 13.33 regen with less haste, but that's because you've moved the finish line closer! You haven't really gained any chi. Ascension at 13.33 regen is less chi per second than Power Strikes at whatever regen you'd have with that same amount of haste.
Of course, power strikes isn't regular, since you get your chi 20s at a time. And Ascension could possibly help in other ways (letting you get a clutch expel harm off a little earlier?). But power strikes gives you more chi at the end of the day, unless you have ridiculously high haste.