I just dont think playing in the unprofessional era,where quality of the opposition varied wildly- nowhere as much allround quality in the opposition as now, coupled with amatuer attitude about the sport, playing against far mediocre bowlers is enough to make up a mere 8-9 pts difference in averages from professionals playing the game at a far more mentally taxing level, against bowlers who are a few orders of magnitude better, in a level that is far more evolved than 50-60 years ago.
its a bit like Alekhein being an equal to Kasparov in Chess or Horatio Nelson being an effective match to Erwin Rommel.
This I find hard to believe, given that the respective disciplines evolve and what was considered 'cutting edge' in Nelson/Alekhein/Sutcliffe's time is 'tried, tested and much improved upon' by the time Rommel, Kasparov,Boycott etc. plied their trade.
I think every single player back in the amatuer era would struggle to keep their record intact if transplanted to the modern era,simply due to the fact that the professional era sees the game being played at a far more cerebral level, with a far fitter crew in charge.
Players with extraordinary records like Bradman, Grimmett etc. may manage to still remain in the vicinity of the cream of the crop from the professional era ( in case of Bradman, he was so far ahead that despite a drop in performance due to more challenging conditions, he still would've been the best) but players who were in the same ballpark statistically ( Sutcliffe, Hammond, Viv, Tendy,Lara, Gavaskar, etc.) would most likely be left in the dust by their professional counterparts. This is the logical extrapolation i've come upon.