Hmmm... Unless I am mistaken, it seems like my expression of general "likes" was almost entirely about criticisms I had regarding the latest iteration of psionics in UA.
Okay. I looked back at your post and didn't see anything specific as far as issues. You say it's gimicky, which is a judgement I can't actually answer for you, and that the other features offend your opinion that psionics should be more controlled. I don't have either of those issues, so I don't see how I can adequately refute your assertions of your preferences. I'll try:
Gimmicky: the psi-die is very similar to the battlemaster dice. The effect is on the same order and you can choose to use it or not as you want. Using it may or may not achieve the goal you want. Design-wise, it's not more gimmicky than existing features, with a different flavor. So, no, I disagree it's too gimmicky -- it appears to be just gimmicky enough to fit in with other 5e features.
Losing the die on a high roll is not rewarding: Well, I flat disagree, here, as I would not feel that unrewarding at all. The die doesn't expend at all unless you get maximum effect. To compare to the battlemaster again, those dice are expended no matter what. So long as I don't roll maximum, my psi-die is always available at the same power level. If I do get maximum effect, that's the only time is expends -- ie, I only lose the resource after it's had maximum effect, never on minimum or average effect. That isn't unrewarding to me at all, it actually makes the feature more available.
Lack of control due to random die size changes: I can see where you're coming from, here, but I don't think it's as random as you're saying. I get the choice to risk my psi-die with full knowledge of both it's current state and the odds on that use of it degrading or improving. It's entirely transparent to the decision making process -- I have full information on what I'm risking and the range of outcomes. Plus, I still have the reset mechanic to fix any bad luck runs (at least once). While, yes, the mechanic is based on a random outcome, it's use is anything but random -- it's choice to get a benefit added every time with full awareness of the risk envelope. This, exactly, is the kind of design I like -- presenting the option for a risk to players that is 1) fully understood and 2) even if it costs the resource it's always of benefit when used.
So, yeah, I don't agree with your criticisms, either in the flavor presented (which I have no baggage for, so isn't a concern of mine) or in the specifics of how it operates. The "gimmick" isn't far off of existing designs that are well liked (superiority dice) and I view it as far more controlled than you do because I'm looking at the choice points, which are clear and unequivocal, instead of the mechanic which is random. My choice to engage the mechanic is very controlled, even if the mechanic is random. Just like attacking, or using a superiority die, or action surge -- I know what using it can result it even if I cannot predict the results.