If ya didn't notice, my moveset doesn't have Synthesis. Giga Drain won't heal sufficiently on certain pokemon (Grookey, Scorbunny, Ferroseed etc.) and regenerator is only if you want to switch out, something I only do against terrible matchups, where I can't hit super effectively. If I do not decide to switch out against a Pokemon that Giga Drain can't hit effectively, I have no way of recovery, other than leftovers. I also have Toxic so I need more turns. I said as well that I find lefties more helpful with my particular play style, tactics, and rest of my team. Feel free to use Eviolite if that suits you more though!
Hope I helped :)