Regs probably the worst at taking down towers and the only reason he is any good at it is because of the range... if you take that away i think pretty much any demigod can take down the tower faster with less damage done to them. Probably the best would be generals just because they have heals + extra dps + other targets for the towers to take down.
Hell, why isnt Rook overpowered then, he can plop a couple towers down, start hamering on the tower while at the same time drain the tower of health and regen his own all while the tower is basically stun locked while doing so.
How about UB, he can spit on the tower do 1000 dps over time, leave regen health and farm creeps and do it again sure he gets hit for 200-400 damage from the tower while doing so but it doesnt take him long to bring it down like that especially if he feels safe enough to melee it at the same time.
How about sedna, massive health regen + minions, its almost like she can just sit thier attacking the tower all day.
Then you got QoT, she's shielded + a ranged AA and maybe uproot depending on build + minions.
What about oak, he goes invulnerable and spirit swarms the thing oh know its destroyed.
The more you play the game the more you realize its wonderfully balanced. Some players are jsut really good and they make it look otherwise. The only balance issues i've really seen were exploits and they get fixed eventually. Hell back when oak would shield and HoL it was a friggen nightmare killing that bastard twice and sometimes thrice before he actually went down.
Basically no reg isnt imbalanced, if anything he is one of the weaker demigods without a decent team. Though thats true of every demigod... wha... true of every demigod....... that almost soudns like its equall and balanced