Mines arn't fine. They need to be changed somehow. Just compare Mines to Hammer Slam. Mines are harder to dodge, have better AOE damage, can be placed at further range, and have all the utility advantages of being preplaced. Mines also get their slow effect at 4 skill points/level 10; Hammer Slam requires 5 skill points/level 15. Hammer Slam's only advantage is better single target damage in a single use, although for practical purposes that also requires using a boulder roll II (level 10; huge mana cost).
I think it is no mistake that the couple occasions I've played against a high-ranked Regulus, their primary strategy has been a complete focus on mine spam.
Oh come on. Reg is squishy as hell. Rook is not and has other abilities to further increase his ability to defend himself (structure transfer and towers). So Reg had better damn well have MUCH more effective damage dealing abilities.
You cant compare the damage dealing abilities on two DGs that fulfill completely different roles. Reg's main purpose is to deal damage, so yes, he is going to do above average damage. This doesnt mean that Reg is unbalanced.
Given that Reg is countered by many common DGs, nerfing one of his big skills is a mistake. Its an average DG at best anyway.