The greater athleticism of keepers cancels out the current speed of forwards, a ball zipping quicker on today's pristine pitches is far easier and more predictable for a keeper to deal with than one that weighed a ton and got stuck in a mud bath or a lump of snow.
Today's keepers are way over protected in my opinion, the bravery aspect of their position doesn't really come in to it anymore. Even rules like the back pass one helps then enormously, which is great for the current keepers, but something goalies of past didn't have the luxury of.
I watched some old footage of the St Etienne game, and it's marked how players could hardly kick the ball with all their might from the penalty area to the halfway line. When a St Etienne player took a snap shot, it went around 12 yards before dribbling out, and I'm not sure that was entirely down to the pitch. While the ball of the 70s was no longer the leather stitched monstrosities of old, I think the composition was still significantly different from the pingability of today.
Watch that clip of Trent jesting with Lingard and hitting the crossbar, and you can hear the ball go
ping. Maybe it's low quality balls that I played with (and I'm not even counting the Mouldmaster for comparison), but my memory of kicking the ball is a dull clump, maybe a tonk if I connected well.
