Honestly he'd be a much more interesting villain than Tyreen.
Think about it; he's been put down his whole life by his sister, has those crazy siren leech powers, the prosthetic arm, and a following of rabid fans willing to do whatever he says.
He could totally be a viable and interesting villain.
I was disappointed that he didn't pull a heel-face turn in 3 because of all the abuse he received. I'd have him try and leech all of his sister's power to kill her even if it ended up killing him as well due to power overload. The leeching wouldn't kill her but it'd be enough for the vault hunters to have a chance to finish her off.
He honestly could have been the anti-Handsome Jack. Where Jack wanted order and control at all costs, the twins just wanted power and to kill anyone who stood up to them.
Yeah his death (if I remember right) was when I realised that, yes, they have completely fucked this entire story up. He could've been interesting but they such with the utter shite that was tyreen.