You are expecting DFM to be garbage. That's not a good way to start out with a brand new truck. Why in the heck did you buy it expecting problems? It hasn't been available long enough to determine if that is the case or not.
I never had an issue with AFM and neither have hundreds of thousands (quite literally) of others. As you said in the OP, generally speaking, only folks that have trouble post in the forums. A VERY VERY small percentage. Just like the 8-speed trans issues. Never experienced that either. Not saying there were not AFM and 8-speed issues, they just never happened to me or anyone I know for that matter.
Love my 2020 LT Trail Boss. I have the 5.3L. Got the 5.3L because I was tired of feeding my 2018 LTZ 6.2L premium fuel. With the payload and towing exactly the same I saw no benefit to the 6.2L in the TB. Also, I have never been able to tell when DFM is active. Some with aftermarket exhaust say they can tell and they complain of drone and make negative statements about DFM when it was their exhaust modification that cause the "issue" in the first place.
In any case, I wish you nothing but the best of luck with your new truck.