IMO Doc's not a hard-ass coach, and he needed a hard-ass assistant to get all of the new players to know and execute their defense in pre-season, not by chewing up half the regular season.
Because they haven't known or played the defense right, the other players on the team have lost trust in the system and that their teammates are going to be there on defense. Now they've too much experience playing the system poorly and being proven right in their lack of trust in their teammates to get there for them.
Also because Doc's not a hard-ass coach, he hasn't been able to rein in Rondo's worst tendencies on offense, which include making himself and his passing too central to their play. There's a reason the offense has often run more smoothly over the past two years when Rondo hasn't been in the game, and that is because there is more ball movement and passing and creating from the other players on the team.
They've got enough new parts underperforming on this team for me to put much of the responsibility on Doc--and his lack of top-notch assistants to cover for his own weaknesses this year, when top-notch assistants are needed more this year than in the past five.
PS We saw similar disarray after the Perk trade, when Doc was totally ineffective in weaving so many new guys into the team in mid-season.