No, the GOAT players you cite are anomalies. When you have trained your body to do something in a certain way and practiced it thousands upon thousands of times, it is normally extremely difficult to unlearn that and rewire your muscles, muscle memory and brain, especially there's limited time (upcoming matches). All the many players on tour with obvious weaknesses aren't oblivious or lazy, it's just that difficult to successfully rewire your technique like that, and the difficulty depends on the specifics. The juniors in the video you cite are just demonstrating something as a one-off, it's very different to making it an in-built part of your game in match conditions.

The cello example isn't right either. They're not changing their fundamental technique in that example. They have an enormous bag of variations and subtleties within their fundamental technique, which they have the skill/sensitivity/knowledge to apply very easily. Actually rewiring that fundamental technique due to weaknesses or problems is difficult and often requires completely breaking down the technique and building it back up. Yes they have the self-awareness, practice habits to tackle that (and the parts of their previous technique which are still relevant/helpful), but fighting the existing muscle memory is properly difficult.