BCowan,
It is a fair point the putting surfaces were firmer at Augusta in the monochrome era, but you logic falls apart once we take the reasoning a step further. While the surface tension of the greens were more prone to a bounce on landing (watch some replays from the early 60s), Bermuda grass varieties at that time had thick leafs that would today be called extremely grainy.
Since most putting surfaces tilt back-to-front in some measure - and the older Bermuda grasses tended to grow towards the water, down the drain line - approach shots may not have grabbed like today, but once landed, balls rolling into the grain looked like dragsters popping their chutes.
Finding yourself above the pin in that era may have been every bit the challenge as today because gauging the speed down-grain, down a hard slope is a capricious adventure. The new varieties are extremely consistent - regardless of whether you are putting up, down or sidehill. Once you get the speed down, it is all a matter of nerve control.
When Arnie was stalking Augusta, it was harder to roll the ball with any consistency because Bermuda grass does not behave the same way. Many times - when playing on old-fashioned surfaces - a putt would break a certain way, and then a second try would yield a far different result.
If you were to give the boys on the big Tours a choice, 99% would vote for what we have today - no matter how frightening.
P.S. You ever play Oakmont? For member play, the greens are wickedly firm. Try holding your approach shot on #1, #10 and #12. Good luck.