@ByeByePoly how come you haven't jumped on this yet?
Anyway,
@user92626 has a point in that not everyone is too fussed about becoming the best player they can be. Some people would rather reign in 3.0 hell than serve in 4.5+ heaven, so to speak.
However, I do think that the concept of fundamental techniques exist, otherwise analyses of pro strokes looking for common threads would by definition be a fruitless exercise. The source of confusion in this thread assuming I've skim read accurately is that
@user92626 may be conflating techniques that are
correct with techniques that are
appropriate. These are not necessarily the same things, and often they are not.
Now in terms of fundamentals, they may differ depending on the type of shot that is being hit, eg a WTA style forehand as opposed to an ATP style forehand.
But if you were to take a number of pro players hitting a particular type of stroke and you boil their techniques down (therefore evaporating stylistic choices that distinguish one pro's shots from one another), then you should be left with a handful of commonalities that we could reasonably consider as being "fundamentals" or "core techniques"--at least in theory.
We know, for example, that in a semi-open / open stance ATP style topspin forehand, that takebacks are going to be relatively shorter, and rely heavily on rotation from the hips, which are driven from the legs and coiling at the hip, wheres with classic and WTA style forehands, takebacks are generally larger and there is a heavier emphasis on linear transfer of momentum rather than the coiling and uncoiling that is evident in ATP style forehands. But how much of this is considered "fundamental" is going to be rather blurred because pros (just like any other player) will pick and choose or emphasise or de-emphasise elements that best suit their tastes and results, and then there is always the possibility that certain pros may have technical errors or limitations in their techniques (eg the Djokovic serve in 2010, the Nadal serve in 2009). So really the difficulty is being able to distinguish the parts that are actually fundamental from parts that are advantageous but not required, and to point out where agreed fundamental elements are erroneously absent in pro-level shots (as opposed to blindly assuming that it's necessarily technically sound because they are professionals).