There probably was a problem with one or a couple of your apps which drain your battery. You should have installed Wakelock detector or an app like that and check what caused the problem.
If you're among the few who experienced a problem, maybe the problem was elsewhere, not the ROM per se.
Maybe if Xiaomi just helped a little out and published drivers, full source and what not, he could have made a faster one.
I have the uttermost respect for Wajk, he's really dedicated to making MIUI smoother and better for us all!
He also released the WIUI 4.4.4 V6 ROM, based on the leaked one (the one that's slowly turning into the "Special Edition"), which might be faster than what you experience now .
If you do not like it, they'll release the official "Special Edition" in just two days (imma try it out for sure )