maybe you'd have been happier if I'd called it high-impact?
Not really.
McGrath is the greatest 'corridor' bowler of his era, his metronomic accuracy and his impeccable seam position are legendary. We have statistics at our disposal to show that he was extremely successful. But none of that would tell us much about the essence of McGrath's bowling; why a doggedly accurate bowler who has never been the fastest among the quicks, who was clearly not among the greatest movers of the ball, was so successful.
It was not just his style, perhaps closest to Curtly Ambrose, but his tactical acumen that made him so special. His consummate skill, tenacity and intensity in spotting a batsman's weakness, planning his downfall, and then executing that plan with the precision of a grandmaster in chess. Reminiscent of Andy Roberts at his best.
Seeing him bowl reminded me of two of my favourite quotes:
"Simplicity is the ultimate sophistication." - Leonardo Da Vinci.
"Perfection is reached not when there is nothing left to add, but when there is nothing left to take away." - Antoine de Saint Exupéry.
Statistics don't come anywhere close to explaining that; why he was so so special. Nor do appellations like 'Giant Killer' or 'High-Impact'.
Not trying to take anything away from your original statistical analysis. Just that I think that to tell the whole story, any statistic has to be 'explained'.
Except there's no question which is more important to a team's success.
and also there is no question which is easier to obtain
Taking top order wickets is by far the harder task. However, elementary Game Theory 101 would tell us that doing the harder task better than others does is not by itself 'more important' than doing the easier tasks better than others.
For example, if there is a race to the finish over to the top and down on the other side of a hill, the climb is by far the harder part of the route. The competitor who does this part extremely well, gaining a big lead over the others in this stretch would capture our imagination. Just as the cyclist who dominates the climbing stages - 'The King of the Mountains' - is the subject of adulation. However, in the overall, somewhat prosaic, matter of winning the race, the time gained over the others in the 'easy' downhill section is every bit as important.
The percentage of top order wickets taken may be indicative of many other things; but it is certainly not indicative of how effective a bowler was.