What would you propose to do with the increasingly growing cast though? I found already at the end of the game that I had way too many characters in the sense that they are even less important (or get interacted with) than the special NPCs. I think this should be addressed somehow. I basically sacced all the units they gave birth to immediately (except the few good ones), which was just a passive increase in this purple flame thing. Because creating a team costs the same amount of AP no matter what, in the end, we will have so many unusable units (base Hilis etc.) that just get sacced manually that this will become tiresome and tedious in another way.
Although I agree that not being able to properly forward base is a bit of a problem. (Using teleportation is the only thing that comes to mind here. And that will run out eventually. And I guess you can wait until you have colonized a (main) city fully before starting another conquest for later regions.)
Upgrade systems, the Brothel update, potential methods for recruitment...I feel there are better ways to handle such a system, for example:
Rather than a malus if there is no 'relief girl', it could be a bonus : if latter region gets harder (for example, start fielding packs of 8 units, or have some event that could wipe out some of your position (since you have several region already, having your frontline die is far from a big problem, and it would force to adapt to the region you are fighting in you counter that kind of event)), you could use the girl to give units in this position (or even adjacent ones) a small bonus, or have them scout and protect a position from randomly appearing ennemies/bad event.
That would make them relevant, incentivise to spread the one you don't use and if the bonus is tie to the specific girl (like getting a free use of their ability) strategize with it, while not making it a necessity or else.
This is already a much better idea, because it is a benefit rather than a negative. I don't want systems that punish you to pile up, as nothing gets more annoying than when games feel the need to add additional
busywork rather than buffs and benefits. I'm not opposed to the idea of a comfort system, but only if the system does not punish you for deciding to ignore it.
To give an example of a game that did this, Minecraft. As someone who played the game since beta, I hated the change to the food system then and still hate it now, because it turned food from a nice little health benefit to busywork I had to constantly manage. If I want to play a survival game, I'll boot one of those up, but I'd rather focus on tactical benefits rather than having to meter manage for my units to either not die or get weaker. I prefer difficulty to come from how enemies approach us, rather than the focus be from our own units getting pissy at us.
An upgrade system for our breeders would be a better alternative, and as we go into later updates with the whopperflower, riftwolves, brothel, and vishap updates, perhaps those systems could necessitate upgrading our girls. Right now we have the ability to corrupt them into nycto element and breed nycto hilichurls, but perhaps that will be at odds with the different flavors of beast we are getting? So something like priming the girls to birth the much larger and far stronger Vishaps may demand that we do something to them in order to unlock it, which would bring our weaker units back into the picture since they won't be doing much for our main forces anyway other than archer spam.
Mind, this is assuming the dev
wants them to be relevant later in the game in the first place. As you get better girls, your army changes with them, so perhaps its part of the flow of upgrading in the first place. Either way, I personally dislike the idea of putting in meter management beyond resources. I was quite happy when hilichurl management became as easy as it was, and I'd like to avoid unnessessary complications to that, compared to focusing on making enemy units more interesting, or developing new breedable units to customize combat to our liking.
Were I to try and come up with a way to make breedable girls last longer, I'd focus on things such as elemental enhancements, shifting, and pool increases for the sake of turning weaker girls into good options like Alice or Xianyun. We have Nycto corruption as one such example of directly changing an element into another, perhaps finding a way to change elements over so they can breed much more useful units from another tech tree would be a good focus to undertake? Pyro is one such example of being a mostly useless tree for the time being until we get other unit types later. Turning someone like Hu tao cryo instead, or even electro (less relevant when the inazuma update comes out given the metric ton of them we will get, but I'm basing my observation on what we have now) would be a much better use for her until Natlan comes out and makes Pyro slimes relevant.
With that said however, I'm fine even if they choose to do nothing with early units and instead focus on the collection aspect. My interest lies more in the later unit additions rather than worrying about Amber or Fischl. Why concern myself with them when we will be breeding literal gods later? Or bombshells like Clorinde. Vishaps, on the other hand...There are a lot of things one can do with an army of lizards...