They were not alone with numerous other players also guilty of lapses in concentration but McFadden was unable to explain his side's collapse or why basic mistakes had crept back into their play over the past month.
"It's just not good enough at this level and its pretty average to be honest with you," said McFadden.
"We defended well for periods but we just had individual lapses and they were costly.
"That's our season in the last month, it's just errors."
The Warriors had some late changes to their line-up with Vatuvei starting the game on the left flank after being ruled out through injury earlier in the week, and Jono Wright replacing centre Blake Ayshford who missed the game through illness.
Ken Maumalo, returning to the right flank after a week out with a hamstring injury suffered in the away loss to the Cowboys, also had his handling problems and was caught out defensively by his opposite Semi Radradra.
While his side's combinations and cohesion may have been affected McFadden refused to blame the positional changes for their mistakes, saying: "The changes don't make people drop balls.
"We've got to be better than that. It makes it more challenging but it's not an excuse."
He conceded his side has some issues with the mental side of the game when things are going against them but declined to name names when asked if the same players were continually letting him down.
"I don't think I have to answer that question," said McFadden.
"There's probably an element to that (mental struggles).
"Confidence can play a big part in that but that's why you need to have that reliable skill set and ours isn't at the moment in individuals."
Captain Ryan Hoffman felt the performance summed up the Warriors rollercoaster campaign in which they were often their own worst enemies.
"Today's game was a great example of our season," Hoffman said.
"We showed that we can do great things and then we just allow teams back into it.
"We get ourselves into position to be competitive in the game and individuals lapse and that hurts the team."