Basically, what he's doing is perfectly within the rules. Overspecialization is a balance issue when players make their characters. If i were to have a troll physical adept in my game with a build like that, i'd want to make sure he feels useful, but also make sure he's not overpowered in relation to the other characters. "But he is overpowered." you say? Well, here's some suggestions i'd make to keep him in line.
Make sure to have one (if not more than one) long-range shooter in every major encounter that shoots at him and him alone, hes the biggest target and the meat shield, the biggest threat in the group at first glance. Also I'd make sure any indoor encounters would take place in open areas, foyers or large rooms with second story balconies or mezzanines. This will eventually force him to learn to use cover and not just wade out there thinking he invincible.
Have at least one mage in every major encounter, and keep him out of the troll's reach (using things like Levitate and/or on top of buildings or balconies). Mages are a great way to counter physical adepts as they rarely have a high willpower to resist spells. Just the other day i used this against my party's meat shield troll character and the player had never really had to go against a mage before. The mage cast a force 6 clout spell and did something like 11 boxes of damage to him, because he had almost no chance of resisting that spell with a 3 willpower, of course he soaked half that because hes a troll, but the player literally said "wow, no one has ever hurt me that bad before" and he no longer charges mages lol.
To make him feel useful, pit him against several melee combatants at once, three or so with small melee weapons, clubs unarmed, etc. Since he does so much damage in close quarters combat, keep him busy doing what he does best and then let the other party members do most of the actual other work (mages, snipers, objectives, etc) while the troll does what he does, he'll enjoy it and so will everyone else because the troll isnt out two shotting everyone in combat while the rest of the party just watches.
Pit him against other trolls, they dont even have to be physical adepts, they'll just soak a ton of his damage and even the combat encounter a bit. I hate to advise to throw stuff at him to 'just keep him busy' but with a character so focused on one thing, that's what you have to do if you when you want everyone else to have fun. Just make sure you dont go overboard with it if that's not your intention. If that troll adept player can't handle what you throw at him, its likely the other player characters will get overwhelmed by trying to manage his job while they're trying to do their own, but then again, it might be a good lesson for him to learn so he doesnt put himself at risk just because he thinks hes a badass.
These are just my suggestions, feel free to use them or dont, it's jsut what i would do were he playing in my game.
