Potential is pretty straight forward in that the players with better potential can reach better skills because their cap is higher, however potential (like game shape) also varies. For example your player with 7 potential can be anywhere between 7.0 and 7.9 potential, which is why players all cap at different spots in their career even if their potential is the same, along with what you are training. Your guy looks pretty good! I can almost promise you that he should get at least a pop or two this week if you are training 1v1 and didn't get a pop last week. I trained 1v1 a ton last season and neither of my guys had two consecutive weeks without a single pop when training it, so I hope that boosts your hopes a bit.
Murray/Harris/MPJ/Grant/Jokic - 2020 NBA Champs