You ****s just eliminted Italy
English young players seemed to me very phisically fit, expecially for young fellas, but many of them might not be prepared for technically superior leagues and have less of an impact than you would imagine.
Mbappé is a beast, he's made a whole season at a very high level, while Martial (who's also still a talent imo, he's just misused, I'd love to see him play as a sole striker in a team oriented on positive transition, like Arsenal in Premier) made just about half a season before the big jump, he's also already played Champions League matches in a Championship winning team, I wouldn't worry about mental fragility.
Also, is there a soul here that follows Serie A?