My Big Bang Hero build

Drawing dmg to you should be the least of your concerns really when big bang comes. You won't take anywhere near the dmg you currently take from mobs so that isn't even a problem anymore.

That doesn't mean that you won't be taking damage. Why the hell would you forcibly take hits when you can do the exact same thing without taking hits?

The range of slash blast is the same as you using your regular weapon atk swings practically with stabs, swings, and slashes.

No, it's not. Slash Blast has at least double, if not more range than that.

 Spoiler

The only issue is you need to hit at least one monster, which is why Ground Smash is so much superior in Second Job. That issue doesn't exist when you have Monster Magnet, and Rush, and is the same case for Coma anyways. It's a great way to judge if you're going to hit all the monsters you want with Coma. Who wants to Ground Smash/Brandish six monsters together to try to Coma and find out they only hit two out of six because the others were too far away?

Would you really want to use that kind of range constantly? You'd barely hit anything, most of the time only hitting a few targets at most.

The whole point that I even recommend it at all in Fourth Job is to use it in conjunction with Monster Magnet, Rush, and Coma.

I'm not saying Soul Driver is a bad skill and you should never use it. I'm saying it's slow.