I was going to bold-face all the parts of your post with which I agreed, but there were so many there was no point. No, he hasn't given up a two-touchdown lead, but can his defenses be trusted not to do so?
If the NFL is supposed to be the pinnacle of football, then you'd think your coaches would be at the pinnacles of their profession. But as you say, Barry might be a victim/beneficiary of the Peter Principle.
His situational awareness seems . . . underdeveloped.
And no, he does not build a defense based upon players' strengths, I don't think. Exhibit A was not matching Alexander with the M inny WR (Jeffries?) in their first game last year, and the Packers getting toasted.
And yes, Bisaccia's special teams have been underwhelming. Disregard the new kicker and punter; the rest of them are not playing very well.