Assuming you mean Regulus, I'd rather the range on the towers be extended to make his range increase require at least the second rank to make him safe from them.  Lowering his range instead would leave him rather close to melee dgs, which hurts him very badly.

that isn't really unbalanced.   The rook just eats towers with one of his abilities, it him GAIN health while destroying a tower.   You gain a significant amount too.  That ability doesn't cost much MP and has very low cool-down time.   So you basically can spam it on a tower to bring it down very very quickly.   I don't think reg has any more power than rook in that aspect.

  Reg's scope also doesn't work on archer towers or  fortresses until level 3 (arrows have longer range than beams I guess).  If you are a player and you're letting Reg sit there and ping away at your towers (which is slow at low levels) without at least going and harrassing him, you deserve to lose a tower or two.

I think instead of nerfing regulus or rook, instead a dark dg or two should gain some kind of ability that would allow him a similar capacity (maybe a torchbearer comet spell or something that has a long cast to discourage use against players but that does great in a siege situation; I expect it'd have a longer cast range than his other spells, but would need a way to warn players that it is inbound, maybe a glow on the target area or something, so they can evade it).

TB's Fireball has bigger range than towers and is quite spamable. Frostnova freezes towers so they can't shot back, great for troop support.

QoT has uproot, which has bigger range than towers and does good damage. Also its buffing itself with compose (is that the name?).

UB's acid spit has bigger range then towers and does nice DoT damage.

I think its quite balanced on abilitíes. The one thing Regulus has is the range on autoattack. But i dont think it a big problem.

Edit: Typos.

They do damage towers.

The time Regulus needs to destroy a tower is time he doesnt kill DG's. From my tests with Regulus i think its a bad strategy to waste your power on towers, especially if the first tower health upgrade (only 600 gold) is in place. Thats just IMHO.

But to support you, i would suggest to increase the tower range by 2 for the first and third tower damage upgrade you can buy. That way Regulus can still be a tower destroyer, if he dedicates more than one level to it. And the opposing DG's can counter it for the first few levels, if they want.