I don't understand something.. you're under warranty, Mazda recommended the catalytic converter be replaced, then they recommended that a catless midpipe be installed (which is not road-legal, by the way), then they couldn't get the CEL to go out (which should not be surprising), THEN they recommended an autozone cat (which isn't going to live long). Is there a reason they didn't just install a replacement Mazda cat?

Agreed that their ability seems lacking, but I'm not even sure what problem they're trying to solve any more.

I'm sure selling that midpipe won't be difficult, they're good units.