The question becomes how good can he be?
Judging by the 27.6% he's hit in 28 Big 12 games over 2 seasons, I'd say Angel making 1/3 of his 3s would be pretty good.
he's better than that. he's hitting 80% of fts and was hitting 75+% for much of last year before fading later in the season. ft shooting is the best measure of shooting ability, so we can safely conclude that he's a good shooter. it's much more subjective, but just looking at his shooting form, he gives the appearance of fine shooter. he also evidences range, which indicates shooting ability. finally, i haven't seen hs % stats, but he certainly put up scoring numbers, which at his size is hard to do without hitting from outside.
translating the ft% to in-game three point shooting, you'd expect him to suffer a little because he has a slow release and needs more space than many shooters. accordingly he's going to shoot more from farther out, and more closely contested shots than might otherwise be the case. his height also contributes to that. still, i expect him to finish at 33% or so this year. in the coming two years, i expect a minimum of about 35% on 200 attempts, adding about 1% to his average for every 30 or so attempts less than 200 that he takes.