So, What are your all's thoughts on whether we have to use Appendix Q for ATR as well as QM?

My impression from my reading was that ATR rules should be followed on their own, and Appendix Q were essentially the next steps (or clarified steps with increased effort) to meet the QM rules, but someone posed the question and it got me second guessing my original thought.

I agree. This is probably a huge simplification, but in reading and talking with others it appears that the ATR general rules typically would be used for non-QM loans whereas appendix Q would be used to meet QM requirements.