Richard appears to have been a good secondary coach, and he seems to have more charisma than Bradley or Quinn did. But I don't think the change at DC should be overlooked. Quinn was legitimately one of the more gifted defensive coaches in the NFL. I know it's Pete's defense and all that, but the defense immediately went to another level when Quinn took over for Bradley, and even before that, our defensive line talent development was on a much higher level when Quinn was on staff.
Richard is going to have to be a hell of a DC to replace Quinn, who was good at generating a disruptive pass rush with four or five rushers and knowing when to (rarely) send more than that amount.
But personnel wise, yeah, I mostly agree with the OP. You look at the rosters side by side and the talent and depth this year defensively is the best ever, though with more question marks.