Pre-war batsmen did not suffer a multitude of serious injuries despite:
a. playing with less protection;
b. against more frequently taken new balls; and
c. on wickets that, in general, were not as well prepared as they are today.
Given the above, it is safe to assume that bowlers of that era were not as threatening as those of the last 30 years and, as such, it is not fair to compare batsmen from the 2 times.
Likewise, whilst I agree that there were a number of great fast bowlers in the 80s, they also had the advantages of:
a. more frequently taken new balls;
b. hand made balls which generally had a more pronounced seam than today's machine-made variety;
c. more bowler friendly pitches (in Aus, Eng, and SA) at least;
d. the unlimited bouncer rule; and
e. more rest between matches.
Given the above, one cannot unequivocally state that Marshall is greater than, say, McGrath or Pollock and likewise one cannot state that Hayden would certainly fail against that era's bowling despite being amongst the most successful of this decade.