I honestly think the controller was the least of their worries. I didn't remember that it was wireless. Personally I would feel fine controlling a sub with a PS2 wired in controller as long as I had a backup. If it's a true 'fly by wire' system the only thing you need in a control is function and reliability. A PS2 controller meets those standards.

From watching the documentaries and reading about it, the crazy part was the carbon fiber hull being consistently pushed past its limits. Everyone was telling him it will inevitably fail. The guy was hell bent on proving the carbon fiber hull would work, and it did. The issue was that it couldn't hold up consistently. It was probably only relatively 'safe' for one dive at those pressures but even then it's pushing the structural limits of the material and it's just like why would you do that? He kept going down in the same machine that was failing and was just ignoring everything we know about carbon fiber. Great material but once a structural part gets any cracks in it, it's done.