The outspoken Italian reckons the Black Cats were not fit enough, not working for each other and not playing good enough football last season.
But Di Canio is predicting better things to come after a whirlwind summer which he hopes will make sure there is no repeat of last season’s relegation battle.
He has already signed nine players, off-loaded 10, instigated rigorous training regimes, tried to instil a different mentality and changed the backroom staff.
There are concerns that Di Canio has changed too much, too soon but he insists change was necessary after the decline of the club under old boss O’Neill.
The former Swindon chief said: “Obviously we made a revolution. I wasn’t worried at the beginning and now even less so because I’ve seen the lads working so hard.
“It takes a bit longer but I’m very happy. I’m not worried for the future.
“We’re still in the middle of pre-season so you can’t say the team is 100 per cent fit.
“But you’re going to see straight away a team that plays together and tries to play football. It didn’t happen last year.