While pressing 123 vs 111 might not make some huge difference in "complexity"(although it certainly does some), the main thing is how it affects "engagement" - which is what actually matters 100% of the time when it comes to game design. When people ask for things to be more complex, it's not really about some stupid bragging rights and ego of "playing a harder thing" - it's about the difficulty providing a challenge and thus more engagement. Sometimes things can in fact be more engaging without being considerably harder, just like some difficulty might occasionally not be engaging but only annoying.
You might not consciously realize that, but for your brain moving the finger slightly before pressing another button is a bit more stimulating than just pressing the same button over and over and it helps with engagement. We can already see this issue on a smaller scale in how plenty of people dislike the "press this button 5 times in 10 seconds" buffs on many jobs and on a bigger scale with how many more people hate the new healer "rotations".
Now, there are absolutely games with consolidated combos which are actually more engaging than the FFXIV combination system. There are games which only allow for something like 8 or 10 skills on your hotbars at the time instead of the "piano rotations" of this game and somehow manage to make their combat systems feel more complex and fun.
However the difference is these games usually have way faster gcd speed(if any), more branching in their combos, more reactive class mechanics(proc based combos, generally procs being a game mechanic instead of "job identity"), more dynamic resource management, waaaay lower cooldowns(seriously, the fact that 30 seconds is considered a "low cd" in FFXIV is hilarious when you look at other games where 20 seconds is considered "long cd") and not nearly as scripted fights, possibly with some actual reactive dodging involved. Comparing the number of buttons in FFXIV to games with so vastly different gameplays isn't really fair at all.
A lot of people here seem to hope that with less hotbar space spent on combos, devs could add more complexity in new skills, but to that I have to ask - have you paid any attention at all for the last four years? The current game direction is definitely not suggesting anything close to that, in fact SE is rather hell-bent on removing any sort of difficulty from the jobs and streamlining anything remotely demanding. It's already started to a degree with transition from HW to SB, but for SHB it's practically the theme of the entire expansion and it's doubtful that it'll change anytime soon - especially with all the blind praise and new players the expac has brought just because the story was great.
Many of us just don't believe at all that devs would use the consolidation for anything interesting and for a good reason, so we want to at least keep any tiny bits we have left.