100% a talent issue. But, in addition to the defensive troubles outlined below, there was a lot of general issues, including at least 3 times this year he's said something at his post game press conference that he had to walk back on the following Monday. Add to that the team seemingly getting worse and worse and it was curtains.
Frankly Mayo was put into a bad spot way too early because of Kraft. He liked him personally so Mayo was given the kiss of death without the experience to handle the HC role, especially following Belichick with a roster bereft of talent. I feel bad for him but it was never going to get better here. He's got plenty of money and can do whatever he wants, hopefully he goes back into the media or just enjoys his fortune and family, seems like he has a good one.