As the guy who co-wrote Hitmonlee's UU analysis, please allow me to defend him.
Fake Out + Normal Gem is the wrong way to use Lee as an Unburden sweeper. The correct way to do it is Endure + Reversal- use Endure to drop Lee to 1 HP, activate his Liechi Berry, and launch HJKs like there's no tomorrow. Good offensive spinners are also kinda hard to come by in UU; the only solid one I can think of off the top of my head is Mega Blastoise. Lee does not have to be able to directly beat hazard setters to be considered a good spinner- all he has to do is get rid of the hazards once they're on the field. Of course Lee is slower than Mienshao, which is the main reason why he is seen as outclassed. However, as a Reckless wallbreaker, Lee does not have to be Choice-locked; he can switch between HJK and Knock Off at will. (Reckless Mienshao are almost always Scarfed.) Lee also boasts priority in Mach Punch, which Mienshao lacks. This allows him to muscle past faster special attackers, particularly Heliolisk. He can also tank a few special attacks, while Mienshao dies to anything remotely offensive. Moreover, you don't use Lee as both an Unburden sweeper and an offensive spinner; you use one or the other depending on what your team needs. He doesn't have to do everything at once to be considered usable. Finally, a choice-locked Mienshao can be easy to take advantage of, while switching into Lee is much more difficult. Obviously, Mienshao's Speed makes it the better choice the majority of the time, but Lee still has enough to merit a spot in C rank. I'd personally like to see him in B-, but let's take it slowly.