I would recommend sticking with the 7 ply. Otherwise you risk becoming the Judas of the solid wood gang.
I can loop fine with even harder stuff, so you should definitely be fine with more practice.
The hollowness comes from a contrast between the hardness of the layers. If the core is softer than the outer or intermediaries, it will always feel hollow. IMO, all 5 plies (of moderate thickness) I've touched felt hollow and flimsy. But take that with a grain of salt, even the Force Black feels "mildly" hollow to me haha.