Personally, I prefer the current rigid auto-promotion system as it gives the player an interesting challenge rather than simply bending to the player's will.
I personally find it less of a challenge and more of a nuisance, one which forces a player to adopt a command that they may not necessarily want to use, but this is a matter of perspective I suppose.
it is a simple mechanic to represent the career ambitions of your leaders - in a real military, your LCDRs and LTCs are not content to remain at their rank for 20 years just because you as the player have decided that it would make your life easier, to use an extreme example. The rigidity itself is not necessarily realistic but as a force to push upward mobility even if the player would prefer otherwise I think it works quite well for gameplay - modeling political pressures very simply without requiring a whole new political minigame mechanic is good design IMO.
I believe this is what the optional political reliability bonus is intended to represent, at least in part - all factors, excluding skill/bonuses, that have no tangible effect on an officer's command that can still get them promoted to a higher rank.
IMO this makes the 4:1 ratio much more flexible and desirable for modeling a variety of rank structures, since you can have 4:1 formation command ratios which are not uncommon but equally well you can model 3:1 ratios and still have some extra commanders at most ranks who can be spun off for these more independent duties outside the main chain of command. With the 3:1 ranks I have always found it challenging to maintain a well-rounded OOB and also staff these more distributed commands without some rather convoluted structures.
I don't personally see how having to abide by a certain officer ratio is more flexible or desirable than officers automatically being promoted and assigned on an as-needed basis, which would quite literally accommodate
any and all rank structures a player desires. If they have several formations requiring a certain higher rank, then good officers from the lower rank are promoted and assigned to fill the empty ranks. Realistically, they would find a competent and promising brigadier general and then promote them. Now, if a player wants to use the 4:1 ratio for whatever reason, that's fine, but they could still easily do so under a "promotions as officers are needed" model. The only difference is that promoting as needed, at the very least, seems infinitely more flexible to
all players' needs and desires and, in my opinion, seems more logical - both in terms of reasonability, and, more importantly, fun.
I will also note in passing that we do have the option to promote officers manually, which is additional micromanagement but is an option nevertheless. In this case you can probably just promote from the top of the rank list once or twice a year to cut down on how much checking-up you need to do.
I would argue it is unnecessary micromanagement, and officers promoted this way are oftentimes not replaced upon perishing. If I have a pool of 400 majors, 100 colonels, 25 brigadier generals, but I need a total of 150 colonels and 50 brigadier generals, assuming 4:1 and 10 officers a year for one academy, I'm going to have to wait
40 years before the ratio naturally meets my army structure. This means that, for 40 years, I would have to monitor and manually promote officers in order to maintain the desired ranks of officers.
Another feature in this vein of promotion based on need would could also be a toggle for a certain rank to not automatically be promoted into. I don't really have a need for 4 Grand Admirals in my OOB
Well, if you only have 1 assignment available to the Grand Admiral rank, then an "assign as needed" model would only promote one person to Grand Admiral and promote no one else to the role, as there will be no further available assignments.
This system would completely minimize "officer waste" where you get too many officers of any rank above the lowest. At worst, you'd have too few of the lowest rank as they're constantly being picked for higher ranks, though this could be prevented by requiring a minimum time in rank or something similar. For example, a new major would have to remain a major for X years before they're eligible for promotion to colonel, then X years before they're eligible for promotion to brigadier general, then X years before they're eligible for major general, and so on.