You could question the "generational talent" claims if he was only performing domestically, but he's consistently scoring and assisting at every level of the game, which is always a fair indicator as to a player's ability.
The Bundesliga:
Played: 32
Goals: 17
Assists: 16
The Champions League:
Played: 8
Goals: 2
Assists: 1
For England:
Played 6:
Goals: 2
Assists: 2
Plus tonnes of goals and assists for City and England U21's.
Rashford by comparison:
The Premier League:
Played: 31
Goals: 17
Assists: 7
The Europa League:
Played: 8
Goals: 2
Assists: 1
For England:
Played 6:
Goals: 3
Assists: 0
Rashford holds his own in the goal-scoring department, but Sancho leaves him for dead where assists are concerned.
Rashford is considered to have had a very good campaign, with pundits, the media and fans praising him left, right and center, yet Sancho has surpassed him after playing at a higher level (the CL).