To me, that reads as revisionist history. MM repeatedly refused to comment on what the other team was doing, indicating he would "look at the tape" and "clean things up" between games. It's one of the things which used to infuriate me about his coaching. He was every bit as slow to adjust as most other coaches.
In the larger context, I do think MLF has a point that the system puts players in a position to make tackles...and it is not the coach's fault when a player fails to make a tackle (unless you believe an NFL player has gotten to that level without being coached on breaking down, wrapping up and the mechanics of tackling a ball-carrier...and I will add in leverage, pursuit angles, and forcing the ball carrier back towards teammates, etc.). You can have your fastest LB spying on the QB, but if he misses the tackle and Hurts runs for 20+ yards afterwards, it's not a failure of design, but execution.
I don't think Barry has done a good job as DC, in no small part because the soft, zone coverages he seems to prefer fail to align with the strengths of his secondary. There were news stories earlier in the season about players (starting with Jaire in Week #1) wanting to be more aggressive. Players not trusting the scheme and the collective lack of confidence, compounded by losing, injuries, and the offense's struggles meaning more time on the field, tracks with the inconsistency we've seen with the defense. I don't think that gets solved during the season, outside of increasing the reps for the guys who are showing effort (Ford, Enagbare, and Nixon among others).