I watched a recent cricket podcast that included Curtly Ambrose and Courtney Walsh. Michael Vaughan asked them regarding modern workload management, and both of them laughed and criticized those policies, claiming fast bowlers need to bowl continuously to maintain true match rhythm. I have heard these exact sentiments from Kapil Dev, Michael Holding, and Wasim Akram.
Fast bowlers and every cricketer, for that matter, indeed require rest to perform their best. These legends making the point is also valid that one needs to keep playing to stay in rhythm, but sometimes I feel it's their ego speaking for them. These guys are legends no doubt but they are somehow jealous as well, because they never got the recognition since they played in a different era. So by ridiculing the rest theory, they are basically telling how hard-working they were in their time.
It is true that perhaps too much focus has shifted from abilities to fitness. Sachin was never the fittest, and with all due respect to him, he might fail the now-popularized Yo-Yo test, and in fact most legends would, even in their prime. Cricket isn't UFC where you need 6-pack abs and 16' biceps to play the game. Take Chris Gayle, for example; he's the best T20 batter but perhaps won't pass any of these fitness tests.
Cricket, I feel, is heavily influenced by glamour and because most cricketers get ads and brand endorsements, they have to be good-looking and muscular rather than being suited to the skills required to play the actual game.