Not just us, in general biggest transfers almost never pay off.
According to transfermarkt in history there were 12 transfers over 100m euros. 9 were total busts, Mbappe was worth it and we can argue about Neymar in PSG and Bale in Real. I would say Neymar is also bust because they never won CL and for sure they would win their leagues without him. Bale scored many important goals for Real so let's say he was a good buy. Nevertheless horrid record for these expensive players.