The argument is silly to me. No matter what hand you use, whether your thumb is in the ball or out, whether you take 4, 5, or 6 steps, and whether you use a wrist device or not, you still have to hit a target with proper speed, revs, tilt, etc. None of the aforementioned items guarantees your success. There are two-handed bowlers who stink. There are people who wear wrist devices and still put little to nothing on the ball.
A few years back, I tried to learn two-handed bowling. I stuck with it for a year, and I improved a great deal from beginning to end; nevertheless, I was still a far better one-handed player than I was a two-hander at the end of that time. Yes, there were times where the extra revs of two-handed bowling allowed me to play the lanes differently than other people, but that didn't matter unless I could actually throw good shots while playing there. Too many people look at no-thumb bowling, wrist braces, etc. as some sort of guaranteed advantage. If there truly were a single factor that gave you an automatic boost right off the bat, EVERY high level player out there would be doing that thing, whatever it was.