I believe you've posted comments like these before and I don't think you've got it quite right. I think you've said that the WI pitches during Marshall's era were a mixture, some spicy but others quite flat. Believe it or not, as a Kiwi who lived through that era, the NZ pitches during Hadlee's heyday were also like that: the odd minefield, some green ones but also some pancakes. I can remember many times screaming at the TV during the early eighties until the end of Hadlee's career something like, "FFS, you've got the best seam bowler in the world who can land the ball on the seam at will. Why in God's name are you giving him these grassless pitches to toil on?".
Just to back up what I'm saying, consider this: if Hadlee had been given greentops regularly during home tests, do you think that his home bowling statistics would be significantly worse (as they are) than his away stats?
Home bowling stats:
View attachment 42706
Away stats:
View attachment 42707
You can see that, apart from Econ, his away stats are better across the board (note that the home and away bowling performances are nicely balanced at 43 matches and 75 innings each!):
Average: away better (lower) by 5.4% (21.72 cf. 22.96)
SR: away better (lower) by 7.7% (48.9 cf. 53.0)
WPM (and WPI): away better by 14.4% (230 and 201 relative to the same divisors because of the equality between home and away)
Econ: home better (lower) by 2.6% (2.59 cf. 2.66)
BBI: away better: 9/52 vs. 7/23
BBM: away better: 15/123 vs. 11/58
5WI/I: away better by 40% (21 cf. 15, same divisors)
10WM/M: away better by 100% (6 cf. 3, same divisors)
It's true that at Notts, greentops were deliberately prepared by groundsman Ron Allsopp for Hadlee (and Rice) and this is reflected by the difference in Hadlee's home and away bowling stats there:
home average: 12.96
away: 16.54 (still remarkable)
(thanks again to Coronis for this home and away split!)
So again, if greentops were the norm for NZ pitches during Hadlee's time, you would expect to see this sort of difference between home and away in the stats and you don't.
You've mentioned McGrath thriving in the batting era post-2000 (and he did). Here's the aggregate batting stats for that era until McGrath retired (the final seven years of McGrath's career):
View attachment 42708
You can see that the batting average is historically quite high at 31.49, confirming the batting era.
I'm now going to look at the corresponding final seven years of Hadlee's career. This was when Hadlee was at his best, exclusively off the short run, ascending to #1 in the rankings, taking wickets left, right and centre.
Here are Hadlee's bowling stats for that time (home and away combined):
View attachment 42709
I'll now do a home vs. away check again (for these final seven years) but first I'm going to show you the aggregate batting stats for NZ pitches during Hadlee's final seven years:
View attachment 42710
You can see that the batting average is 32.65, more than 1 run greater (1.16 runs) than the global batting average of 31.49 during McGrath's batting era post-2000.
Here are Hadlee's home and away bowling stats during his final seven years:
Home:
View attachment 42711
Away:
View attachment 42712
Notice how much better Hadlee's away stats are than his home stats: they're miles better! His away average is over four runs better than his home average! Those super-juicy, super-spicy lush greentops that the NZ groundsmen eagerly prepared for Hadlee test after test don't seem to have helped him very much. Luckily, Hadlee did most of his bowling during his final seven years in away tests (27 tests and 47 innings away compared to just 19 tests and 30 innings home) so bowling at home on those allegedly helpful pitches (some genuinely were) didn't damage his stats too much.
Here's another detailed home vs. away comparison, for Hadlee's final seven years:
Average: away better (lower) by 18.6% (18.44 cf. 22.65)
SR: away better (lower) by 15.2% (44.7 cf. 52.7)
WPM: away better by 38.3% ((167/27)/(85/19) - 1)
WPI: away better by 25.4% ((167/47)/(85/30) - 1)
Econ: away better (lower) by 3.9% (2.47 cf. 2.57)
BBI: away better: 9/52 vs. 7/116
BBM: away better: 15/123 vs. 9/151 (never took a 10WM at home during his prime years!)
Note: Hadlee took 3 10WM at home: against India in 1976, against England in 1978 and against the WI in 1980. He bowled extremely well for these returns and they were all off the long run but they weren't achieved when Hadlee was in his prime epoch, and it was when the NZ pitches appeared to be more helpful to bowl on (see below).
5WI/I: away better by 80.9% ((17/47)/(6/30) - 1)
10WM/M: away better by infinity % (6 cf. 0)
Another thing, Hadlee won eight Player of the Series awards in 33 series and six of these were during his final seven years, all of the six in away series (3 vs. England, 2 vs. Australia and 1 vs. SL).
Finally, the Steyn comparison: these are the aggregate batting stats for SA pitches during the Steyn years:
View attachment 42714
Again, the NZ pitches during Hadlee's final seven years (the prime years):
View attachment 42715
Now the NZ pitches during the pre-prime Hadlee years:
View attachment 42716
You can see that based on batting average, the Steyn home pitches and the pre-prime Hadlee home pitches appear to be about equally helpful but during the last seven years of Hadlee's career, the NZ pitches appear to be distinctly unhelpful and this is backed up by some of the bowling stats I've posted above (and by my now rather vague recollections of these pitches).
The point I'm trying to make is that Hadlee cemented his greatness during his final seven years and the home pitches he bowled on during that time do not seem to have helped him too much and don't detract in any significant way from his achievements or his legacy.