Goals from Pelly-Ruddock Mpanzu, Danny Hylton, Kazenga LuaLua and Luke Berry saw Luton stroll to a comfortable victory with Rovers turning in one of their poorest performances of the season.
"We were just not good enough,” McCann said.
“We lacked energy, we lacked tempo and we couldn’t pass from A to B.
“We were just not at the races.
“Luton were physically stronger than us. They rolled us, they moved it quickly,
“We lacked any sort of skill to get it up the pitch and try to take a chance.
“That’s probably one thing we haven't seen this year. We saw it at Charlton, another game away from home where we were nowhere near.
“You’re going to get that in a season. Unless you’re Luton, Sunderland, Barnsley, teams like that, who have the consistency in their play and the budgets to bring people off the bench like Luton did today.
“They’ve got that consistency, we haven't and that is why we’re floating around the play-offs now.”
Passing play from Rovers was particularly poor with Luton dominating the midfield.
"We were miles away,” McCann said. “From minute one, a set play came into our box and we didn't pick the left back up with a free header.
“From then on we were second best.
“Luton are a top team but we were absolutely nowhere near.
“They’re a good team but we made it very easy for them.”