We fail to stretch teams not because our players arent fast, physically we have one of the best teams in the Prem. We fail to stretch teams because our movement is poor, players have very small tactical understanding, ability on the ball, ability to move the play. We could field in de Gea, Valencia, Smalling, Bailly, Shaw, Pogba, Fosu Mensah, Mikitaryan, Lingard, Rashford, Martial and still not stretch teams.
It's not because the player would be better than Mane, but the type of skillset you need to succeed in the CL. The skillset of Real, Juve, Barcelona, Bayern, PSG is so much better than any PL club, it's outrageous. We rate pace, running power far too much here in the prem.