It's not really clear to me what you think the the underlying problem with fighters is though other than that you think they don't fit your personal perspective of what fighters should do, especially since you touch on all sorts of suggestions including AI changes.
They don't counter bombers or each other. So, because of this, they are essentially just bombers themselves- just infinite ammo bombers. You are advocating making them "weak bombers" for this reason. But if the AI stays the same, then the line between interceptor/fighter/bomber is practically nonexistent as far as behavior is concerned. Interceptors only fight each other when around the enemy or allied ship. If they are weaker to PD, then their clashes around ships are more meaningless because the real threat is the PD guns and not the interceptors themselves. As I have stated before, I'm not even saying you can't weaken them defensively. They may need that
and limited ammo to become more balanced. But, none of that will make fighters feel good- especially compared to bombers- until fighter and interceptors have a role that isn't just being another bomber that sometimes "fights" other bombers briefly before settling back on the target.
So my question to you is, what do
you think is the role of fighters and interceptors? How would you use them?
Would you use them? If they are just "weak bombers" then people will just equip actual bombers and ignore fighters- we have already discussed why less OP is not enough of a reason to make them attractive if they are just bad in comparison.
All of my suggestions have a purpose. They are pieces of the same puzzle. If you would like me to explain that further please let me know.
It is the intended purpose of the suggestion of changing hull and shield values is that fighters will die faster. So that is not a problem that they will at all. There may be a sharper tipping point between being useful and dying but that can be fine too.
How is that fine? Would you be ok with that design if it were like that for frigates? I suspect not...
*EDIT*
An alternative is to change the fighter replacement rate.
Forgot to respond to this point. Ironically, it just so happens that this was the second balancing mechanism of the new .8 fighter system I tried when attempting to combat fighter spam in .9. To break it down:
There are two ways you can do this:
1) Reduce fighter and interceptor individual replacement rates so they take longer to replace a wing member.
2) Reduce the minimum threshold cap for replacement rate as it decreases.
(I guess you could also do both if you really wanted to. If the replacement rate threshold could go all the way to zero, that would make fighters more in line with vanilla missiles as a concept of limited burst damage- with a weird mechanic where as long as you don't let it get too low it could theoretically be infinite... Not only would this direction also probably require a lot of AI changes so that fighters aren't wasted (missiles have already gone through this transformation), it practically reeks of player abusiveness leading to unexpected power creep without some serious AI nuance. If AI refinement is the concern, then this suggestion would be even more work.)
To discuss this, an overview of how replacement rate works is required. I believe that replacement rate starts to decay if any wings are under ~50% members? (Someone correct me if I am wrong) What effect does this have? The longer it takes to replace an individual wing member the more impact that wing has to replacement rate when the wing takes losses over the threshold. This compounds upon itself because obviously the continuous lowering of replacement rate further hurts the wings' ability to replace their members and get above the threshold where replacement rate begins to increase again... so in effect this means bombers are often the hardest hitting factor on replacement rate and losing a bomber wing can mean the replacement rate goes from 100% to remaining at 30% the rest of the battle.
If fighters are changed to take longer to replace each wing's members, then fighters are more closely aligned with bombers in their effect upon replacement rate. So, instead of having a more nuanced system where bomber-based carriers are more easily handicapped by being stuck at 30% replacement and fighter/interceptor-based carriers have more of a wax and wane effect as they take and replace losses, all carriers just quickly get to- and remain at- 30% replacement rate for the majority of the battle. So this further emphasizes the "fighters as bombers" role the system already encourages.
How does this solve mass fighter spam? It does nothing to really reduce the staying power of the fighters themselves compared to bombers, because fighters still have infinite ammunition while bombers do not. The unstoppable fighter waves may come less often- or even only once considering the exponential effect replacement rate has- but this results in two and only two scenarios:
1) The first and likely only wave focuses on a single target and beats it handily- then moves to another and does the same- then moves to another and does the same, etc. Massed fighters are still optimal.
2) The first and likely only wave focuses on a single target and takes enough losses to weaken the swarm before the target dies. The swarm moves to the next target. Gets weakened further and takes out the target or dies. Either way, fighters are no longer useful for the remainder of the battle. Carriers sit there as useless paperweights and may as well be retreated (leading to player strategies that never let the carrier die while AI carriers get slaughtered.