Your right the reason Boro fans have been staying away last season and in was due to poor management, as most Boro fans are sick to death of a new manager starting his career at the club and then fans paying good money wondering which team will turn up, I'm not really bothered if Sunderland do get more of a crowd than Boro and tbh the argument can't be justified as
1) Sunderland play in a lower league, so always going to be considered one of the teams to go back up. 1) Sunderland also plays 2 more games than Boro do. 3) New Manager and Chairman, so bumper crowds where always expected, try having new manager after new manager with the same promise of 'taking the next step forward' and failing to deliver and then see if the fans don't disappear.
Enjoy the sell outs for next seasons relegation and being a yo-yo club, lets hope this time you can at least get more points than last time and stay where you belong, outside of the Prem, if you think that your going to be in the top 10 or push for Europe might want to think again, its one thing being new manager and playing in the Championship but its a whole new ball game and harder in the Prem.