The obvious caveat to that is harder leagues (for Vietto definitely). But I agree with what you are saying, a 19 year old with a 1 in 3 rate is really good, considering how good he is in other facets of the game also.
That could be an answer but the french league isn't an 'easy' league, it's a boring league. Just think about this Ayew, Diafra Sakho, Gomis, Aubameyang, Gomis or Giroud.