I wouldn't have played him any more than Cal did - FWIW. He was good for energy, rebounds and occasional threes but had no handle whatsoever. If he didn't like how he was used then I'd say he wasn't being realistic about his abilities and contribution as compared the the talent he was playing with.
You nailed the problem right there. Gabriel was a face-up player who had 0 ability to do anything off the dribble. In modern basketball, that leaves 2 options for him, a small-ball 5 (and he's way too skinny for that) or a stretch 4, which is how he was used at UK.
Cal has really only had 2 guys at UK that I think were distinctly misused, and both were out of necessity. The first was Trey Lyles, who was a good post scorer in HS, but was pushed away from the basket simply because UK had better options in the paint (though ironically, it probably helped his draft stock), and the second was Isaiah Briscoe, who was a pure old-school PG, but played with Tyler Ulis and De'Aaron Fox, who were simply better.
Skal was probably misused to a certain extent, but nothing that happened in terms of his role on offense had anything to do with his bad defense and atrocious rebounding.
I think ballhandling is the single most underrated skill in the game. Guys like LeBron, Kobe, and Jordan were all A+ level athletes, but what really separated them was the ability to beat defenders off the dribble from anywhere on the floor. Guys who can't do anything at all off the dribble (and also aren't good passers) are hard to play at any position except center, unless they're elite shooters.