Definitely not a myth. To me, a player has good fundamentals if he can deliver the cue on a straight line and hit the intended part of the white
consistently. By this definition, all the top players have good fundamentals, otherwise they
wouldn't be top players.
I think people mistake 'form' with fundamentals. There are a number of top players with bad form--in pool you have Keith McCready with his sidearm stroke; in snooker you have Barry Pinches, with his awkward-looking stance and approach into the shot. Perhaps the best player with the most horrible-looking form in any cueing sport is ironically a snooker player. In Alex Higgin's famous 69 break against Jimmy White in 1982, he twitches in almost every shot -
https://www.youtube.com/watch?v=y-yCyRPEBxM By today's standards his snooker fundamentals, while good enough to make him a two-time World Champion then, is simply insufficient today to make it big in low-budget, Internet-stream pool, let alone world-class BBC/Eurosport snooker.
So what makes good fundamentals? To me, a good set of fundamentals comprises of individual mechanics that are compatible with each other regardless of whether the mechanic is textbook or not--grip, stance, eye pattern, cueing rhythm and whatnot. Efren Reyes' fundamentals, while seemingly bad to some aesthetically, in my opinion is excellent because all the above mechanics are in total synergy with each other. His very loose grip goes hand-in-hand with his cueing rhythm and eye pattern. If you ask him to grip his cue with all of his fingers while keeping his other mechanics unchanged, it would completely disrupt his whole cue action. Ditto with Alex Higgins--his grip, with the index finger off the cue and pointing to the ground, seemed to work well with his jerky delivery of the cue and twitchy head movement. Bad fundamentals is simply one in which one or more individual mechanics don't work well with each other--the worst fundamentals is one where ALL of the mechanics work AGAINST each other.
GOOD FUNDAMENTALS: A player with a pool stance, smooth cue delivery
BAD FUNDAMENTALS (with aesthetically good form): A player with a solid textbook snooker stance, grip and cueing rhythm, but only looks at the cue ball during practice strokes and final delivery.
WORST FUNDAMENTALS (I can think of): A player with feet next to each other, wrong alignment, eye rhythm all over the place, grips the cue as if strangling someone.
So if all the top players' individual mechanics are in synergy with each other and thus allow them to have good fundamentals, what makes the best player's fundamentals better than the other top players'? Think of good fundamentals as a set of gears in a clock--I can argue that a set of gears made of a durable material (ie metal) can last longer and won't break down so easily than one made of low-grade plastic. Even though both can do its job of telling time, I'd rather purchase a clock made with the former. In pool and snooker terms,
a good set of fundamentals has synergetic mechanics AND won't collapse under pressure.
The reason why Alex Higgin's play deteriorated quite fast is because as his body aged, the nature of his mechanics made it more difficult for him to coordinate all of it. In contrast, Efren managed to play top-level pool for so many years because the nature of his individual mechanics has withstood the test of time better, and most importantly is adaptable--as he aged, his stroke has become more compact and has a noticeably faster tempo, but his eye pattern, grip, stance and cueing rhythm remained relatively unchanged. Whether this evolution in his fundamentals is deliberate on his part is uncertain. Even Ronnie O'Sullivan modified his mechanics--his grip is now a modified version of Alex Higgins' and his practice strokes have become less mechanical and are reminiscent of Mika Immonen's--but his stance, eye pattern and alignment remained the same. His re-emergence as the best snooker player in the world from 2012 till now coincided with, and is a result of, this change in fundamentals and to a lesser extent better temperament.
So therefore my own personal philosophy with regards to improving my game is this: don't change a handful of mechanics in one go. Tinker with your mechanics one at a time, until you find a stance, grip, stroke etc. that are compatible with each other.