Very true, it was the GM Thompson who picked so many pathetic defensive players in the first or second round this decade (Nick Perry, Datone Jones, Josh Jones, Jerrel Worthy, etc.) and McCarthy is not responsible for that poor drafting record.
However, McCarthy, and more accurately his DC Dom Capers (who MM stood loyally by long by his sell by date), also played important roles in the Packers' decision to move on from CB Casey Hayward who then signed for $5M a year with the Chargers and became an All-Pro and to stupidly refuse to play Micah Hyde at his natural position - Safety. When Hyde signed a modest deal in Buff $6M annually, he too immediately made the pro bowl as a Safety.
Thompson is mostly responsible for the year after year of terrible defensive play in Green Bay between 2011-2018 (not one season in top 10 of scoring defense), but head coach Mike McCarthy cannot possibly escape blame for that debacle either.
PS (Packers returned to top 10 in scoring D this season and are currently 13-3).