Most dont adapt to the physicality. There are more players who fail to adapt to the league than make it both as youngsters and as senior pros. See Pedro Poro at Tottenham, Latin American player who looks gash every time he steps on the field yet Barcelona are after him. Veron was another, our Own Crespo couldnt settle here, the list is long. Remember Di Santo, a player signed as a promising teen like most of our purchases, the next Crespo, ended up in lower leagues in UK and europe.
If you cant do the physicality of the league, then you need to be able to rise above it. ie, you have to have skills that mean you dont require to be imposing or strong, folk on here name dropped Le tissier the other day. A guy who couldnt run, wasnt that fit yet had skills to turn and win games all on his own.
now, Do Quendea and stevo have that level of ability? Not shown anything like enough for me yet. They may well get there but they're not Rooney levels of ability and physicality, he was 16 and looked like a tank, broke through 3 years younger than the "next Neymar" Estevao. Micheal owen had more pace than anyone else so didnt need physicality or stregnth etc etc etc...