That's like, the same amount of time it takes to kill him near the Arid Nexus exit, save and quit, and reload.
Killing him with the Runner is easier (especially with a bee shield equipped), plus if you wait to kill him until the Rakks come out, you increase the chances of tubby rakks showing up. .
I have a Lady Fist that can kill him way faster than the runner, and I've never seen a Tubby Rakk in that area
I had 2 tubby rakks come out at once before in that area during the loot hunt when farming for the best version of the bunny launcher. After that, farming for the Badaboom I've seen more than a dozen tubby rakks, usually just one at a time.
As I said, waiting until the rakks come out increases the chances of tubbies. The bigger the badass currently out and about, the higher the chances of tubbies spawning. I remember reading that somewhere in the wiki, I just don't remember where. . --- What's the purpose in owning a Grenade Launcher? The sheer inability to continue life without it ! ! !