Quite honestly, I feel the issue with the M&P10 is not even fully S&W's fault. These rifles are sourced for many parts. S&W does not manufacture in-house the buffer, tube, BCG, trigger, etc.
Now, if you are mixing and matching parts sourced from several overwhelmed suppliers, you can expect some issues. Mix issues from one supplier to another, and you wind up with more issues than you should. Throw in some lacking QC; throw in a little instant recognition via the instantaneous internet factor, and you see problems in real-time, that evening before the manufacturer has even been called.
In the end, YES- it is S&W's fault: They are sourcing parts, and it is their job to be sure of compatibility. To their credit, they always honor their warranty and take good care of their customers.
NOW; as to the issue of which rifle is a better shooter overall? I choose the M1A/ M14. It is designed as a true long rifle, and not a compact modular rifle. Sighting in is a little different. That most important 'feel' of shooting a rifle is more natural with the M1/ M14. The sound delivered back to the shooter is MUCH more pleasant to the shooter of the M1/M14. Take an AR10 and do a mag dump. Do the same with an M1. With no hearing on....... you will understand what I am talking about.
Or, should I say..........
"YOU WILL UNDERSTAND WHAT I AM TALKING ABOUT!!!"