well if all melee are op, rook not being a melee than we have only tb, reg, rook, and qot as underpowered.
i would not agree that reg and rook are underpowered. especially not rook. BUT having a rook in your team afforeds that your mates play totally different than without a rook. rook needs more backup than any opther demigod. but this does not make him underpowered. if the tactics are based on the rooks existance the benefits of him are making up for this disadvatage!
similar holds for regulus but for regulus it is also important to know how to adjust its build depending on the enemies you face. but he is definatly not underpowered but indeed heavly wrong played against good palyers and similar too rook, depinding on the regs skill build needs his mates to have a fitting tactics (e.g. as a sniper in ealry levels his mates need to be more aggressive to make it worth using the snipe).
but as the most players only think and plan their tactics for their own demigods relying heavely on adjusted team-play become the weak point. if you consider the fact that your mates need some teamplay and brain as a disadvantage of rook and regulus than you are right that they are underpowered.
the other demigods are more idiot teammates friendly.