Here's some evidence that UB is OP in some sense.
I usually play as Oak. But I suck as Oak. I am simply not that quick of a thinker, or that much of a multitasker. And Oak requires both.
As an experiment, I decided to try UB for a while. I made a build which I didn't really mean to take seriously. I was just trying a minimalist experiment. The build concentrates on Spit, Inner Beast, Stats, and Plague.
With this build, I only need to know one hotkey--'1' for spit.
And after a small number of games in MP, I'm prepared to conjecture: I'm much better with this than I ever was with Oak. I don't die. My team wins. I even get in a few kills every now and then if my opponent gets greedy.
Okay, you might think, that just means I've found out that whatever style of play I want to have, it turns out the style that actually works best for me is spit-and-run UB. But is this really just a difference of "style"? The difference doesn't seem to be style, but rather, the simple fact that it's much easier to run a character which only uses one hotkey and one basic tactic.
I would think that a balanced game would "punish" (so to speak) such a character. Ease of use should correlate with difficulty in winning. But that does not seem to be the case. I've found it fairly easy to win lanes and lives in combat with spit-and-run UB. I'm going to start trying Ooze UB as well. That will require that I remember 2 hotkeys IIRC. And I'll always be using them in the same order, in the same situations. I predict (I'll report on the accuracy of this) that that, too, will turn out to be much easier than Oak.
To reiterate, the argument is this. UB is much easier to control than many other characters, in terms of number of hotkeys and number of needed tactics. But UB is not harder to win with. But if a character is easier to control, it should be harder to win with it. In other words, conversely, if a character is harder to control, mastery of that character's controls should lead to easier victories than those you get with easier-to-control characters. Therefore, there is a balance issue with UB. It should be nerfed in some way such that less coordinated and quick players can not win easily with it just because it's easy to control.
Make any sense to anyone?