I see this sentiment thrown out a lot, but yes, the general idea is supposed to be that maintaining the correct rotation while focusing on Extreme/Savage/Ultimate mechanics is a skill. If someone is capable of pressing their buttons perfectly even while they're being overwhelmed by unfamiliar mechanics they're just seeing for the first time and/or progging, that should indicate a level of muscle memory/job mastery that can only be attributed to player skill. Now, in Endwalker the focus has definitely shifted away from job complexity into mechanics dancing, so people take the combo gameplay for granted because of how easy it is to execute. But you can probably imagine a world (maybe in previous expansions, even!) where combos are more involved, or the rotation is harder with a heavy focus on oGCD management, or you have more individual responsibilities to juggle on your job (TP and MP management say hello) and more easily picture how even a 1-2-3 combo provides value in creating difficulty that allows for player skill to be expressed. At the end of the day, as minuscule as it is, even a 1-2-3 combo creates more of a skill floor and fail state than mindlessly pressing 1-1-1 over and over.
To tie this in to the topic of the thread, it's been a massive failing on Endwalker's part to shift all of the intricacies of combat into the mechanics dancing while leaving the players with nothing interesting to do. A lot of jobs can basically sleep through the majority of their rotation, because if it's not the burst window, you can bet they're doing bland 1-2-3 filler with maybe an occasional oGCD to dump gauge when at risk of overcapping. And that leads to the sentiment we have now, that "1-2-3 combos are so boring and bland and skill-less, we're better off making them into auto-combos!". Did people forget that healers have been tearing their hair out since Stormblood ended because they've been reduced to 1-1-1-1 gameplay for two entire expansions now? The solution is to move in the opposite direction: make jobs more involved and developed, give them more things to do, and the focus will be alleviated from the extremely barebones 1-2-3 combo gameplay we have going for us right now. Give players a skill ceiling that takes real time and effort to achieve, something to strive for, and people will actually want to engage with the gameplay to earn that mastery — that's hundreds of hours of content right there that EW is severely lacking because of how simplified the core gameplay has become.