Me either, as yet. His career isn't over though. I reckon he can get into Steve Waugh/Alan Border territory though. He is way past Miller in terms of batting, but Miller was an all rounder. Harvey could also be knocked off by pup, in fact, I would almost have him before Harvey as of now. That's debatable.
Again you compare with your peers at the time.
20 years ago there were maybe 5 batsmen averaging 50, viv richards, Sunny Gavaskar, border, Miandad.
Before that Boycott and Greg Chappel.
Today there are more than a dozen batsmen consistently averaging above 50. Sri lanka has 3, India has 3, Under S.waugh we had 4, England has 2 or 3, South Africa has 1 or 2 etc etc.
Also conditions, bats and technology has changed a lot in the last 20 years, Have a look at some of the Don's bats, they were matchsticks compared to the axes used today.
In the mid 1980 to early 1990s, anyone averaging over 45 was considered top notch, heck people are on here telling us Mark Waugh was a legend of the game averaging 42.
That said, he's lifted his form from mid 30s, to mid 40s to close enough to 50.
Sure it was off the back of a triple century, but when you start removing players big scores, that is going to affect everyones average. Further his triple was scored in a game with 3 batsman who about 40,000 test runs experience between them and the game was NOT a draw like some of the boring massive test matches we've had in the subcontinent where several players have had massive innings.
While I wouldn't put him in the all time greats category, nor even in the same category as Border and S.waugh, he's certainly showing enough at the moment to put him in the same category as the other top batsmen in test cricket.
The question remains whether he can perform consistently at this level for the next 3 or 4 seasons at least.