So if you discount the bonus gained with items Regulus is not overpowered compared to any other DG.
Thought I do agree the mines are a bit too powerful. Mines are supposed to be a trap, but the way he uses them makes them more of a very powerful grenade that delivers a big spike of damage.
Even the AI uses them like that more often than not. They've been used that way since beta 2, and as far as I can remember, they have never been OP when used this way (but ironically they were once OP when used as traps). They were not always thrown. In their first incarnation, they were set point-blank. The throw change was made to make them more useful. I immediately noticed the change and the first thing I did with them was throw them like grenades, then came here to talk about it and how great it was. It's like that's what the change was meant to accomplish.
Just because something is used in a way you don't expect doesn't mean it's unintended--and sometimes if it's unintended, it becomes a feature. It's called depth. Everyone complained that Demomen in TF2 were using Stickybombs like rockets, since "they are supposed to be traps", but Valve explained in a blog post that this is intended behavior. Sad that people tend to think if it's not in the manual, it must be an exploit. Mines are still great for setting traps, but if they are ONLY good as traps, then they're too situational and too easily countered to be worth a power pick. The devs realized this in beta 1 and made them throwable.