Kane averages 42 away, and 45 if you include neutral venues. Is that really that bad? It's probably something that keeps him out of the "best since bradman" discussion that smith finds himself in, but outside of that it's pretty miniscule, no? Bloke has 31 test hundreds at 55 in a hard batting era. If you go since the start of 2016 when batting got harder worldwide, his away+neutral average is actually higher (nearly 48). Maybe his away average is more just a symptom of the fact 14 of his first 20 test's when he was still young (debuted at 19/20, up until ~23) where away, and in those he averaged 28 away in those 14 test's.
If kane plays for Australia, or another big nation like that in a more competitive era, I doubt he gets 20 straight test's, mostly away, so young and probably has a higher away average, no?
There's only 13 players in the history of the game who made over 850 runs (the amount kane made) away by the age of 22. Kane's average is the worse of anyone of that list bar ashraful, but I think it shows that alot of players don't actually get the chance to play that much cricket away from home, or in general, at such a young age.