It’s since before the treble.
We won the treble because we had almost no injuries at all. We kicked Cancelo out of the squad and Foden had an injury in the January (caused by Cancelo in training) and Foden had his appendix out in the February. We suffered no more injuries that season. It was incredible how we managed to have an injury record like that, never seen anything like it.
But, even then we had a really small squad and we would have looked short if there were a few injuries in a few positions. After Cancelo left, the only full back we had was Walker, we managed to overcome that with the form of Akanji and Aké (two centre halves) playing exceptionally well at full back.
Like previous seasons, when Agüero got injured in 2020-21 and we sold our other striker halfway through the season (Torres) and played with no real striker - Jesus had decided he didn’t want to be a striker anymore despite the fact he could have been the main man for us there with Kun out. He did mainly play as the 9 but when he mustn’t have fancied it, we played either Foden or Sterling proper 9 or false 9 (neither suited the proper 9 really).
At the end of the season we got rid of Agüero and didn’t sign anyone. We played a full season with the fill-in 9 or false 9s with Foden, Jesus and Sterling… Grealish even played there once. All because of our total lack of squad depth in the striker department.
We managed to win the league in all of those seasons but it wasn’t because we had a well rounded squad with strength in depth in every position. We bought two strikers the next Summer and won the treble! How much did having no proper depth up front hold us back from winning the CL in those previous seasons?
We now have no decent right backs, no defensive midfielders at all with Rodri out and we’re back to having one striker in the squad.