My evidence is more anecdotal than numerical, but experience from previous aviation downturns shows that the last few percent are always the hardest ones to recover. Probably that's the fraction of trips for which people ask themselves "Is it strictly necessary?" the most. From memory, 9/11 resulted in something like a 20% drop in traffic. The GFC was more like 8-10%. Both took a few years until traffic values reached and exceeded pre-crisis levels.
With COVID, peak reduction values were in excess of 90%, with something like -45% in Europe right now, when we're finally starting to see some considerable improvement. So, if the recovery pace more or less mirrors the previous "big things" which hit aviation, it would probably be reasonable to expect traffic volumes staying at 80-90% of pre-COVID for a few years once the acute phase is behind us. Who knows, maybe that was what the forecasters assumed as well.