Guys take a look at this thread:
https://discussions.apple.com/thread/5576561
Apparently some guys are claiming for the screen to dim, you need to sleep/wake your device. Now, this works for me.
But that still doesn't make sense. Things are fine with my older iPad 2 on iOS 7.1.1 as well, and my brothers iPhone 5s.
Another guy on that same thread says he went to an Apple store, compared to their display model there, and saw that theirs was dimming and not his. Apparently, he got a new replacement tablet.
I'm wondering if I should do the same.