Muscle Demon is a solid yes. Much like how the Commander class is a very strong vehicle user with very limited equipment slots when fully built out with passive bonuses the Muscle Demon is a strong physical attacker. Great durable generic for physical attack power. Basically not quite as powerful as a Berserker, but doesn't have the critical weakness to magic damage either.

Devil class is more of a "starter" class where after the carrot life you'd throw a physical attacker through this class for a basic set of +5 HP/ATK/DEF passives while progressing something like sword skill.