Both in the long run, I agree, but it's about return on time-invested at the moment. If he's currently at around 15-20% from 3 he really shouldn't be taking 3's in games, unless you are willing to risk losing some close games and risk missing the playoffs. If he's not taking 3's in games there is no immediate benefit to 3-pointer improvement whereas around rim improvement has immediate value. I exaggerated somewhat, I don't really have a problem with him practicing 3's now but improving around the rim should be a much higher priority. AD and Embiid didn't have the same around-the-rim problems Nurk has so for them it made more sense.