I'll preface with stating that im fairly happy with how things are now.
Right now CR degrades at a set rate. If you get 180 seconds, then in 180 seconds your fight had better be over, or it likely will be at your expense shortly after. What if that degradation rate itself changed according to what the ship is doing? What if that rate could vary from 0% to as much as 300%, or higher if balance suggests that.
for example, to pull numbers from nowhere:
actively maneuvering = 5% for 1-2 seconds
Speed = 30%, based on current maximum
shields on = 15%
weapons firing = 15%
current flux = 100% as a percentage of maximum flux.
venting = 15%
overloaded = 25%
taking fire = 15%
hull damage = 2x damage%
It can peak at 405% using those values. it can also be as low as 0% depletion if you just sit there and do nothing.
Weapons fire and hull damage are a bit different from the others, so I'll elaborate.
Weapons fire is a percentage of total ship's OP in weapons that just opened fire. So if you have 100OP in weaponry, and you just used two weapons that have 22OP each, then your used OP is 44%, out of 15% for maximum weapons loading, so 6.6%, for the entire duration that those weapons are loading.
Hull damage is simply the more your damaged, the faster this ticks by. If your at 90% hull HP, then you have 10% damage, so you suffer 20% more depletion.
So a frigate, given 180 seconds could:
Sit there indefinitely
Fly around for 514 seconds if constantly maneuvering and full throttle.
Fight, assuming full throttle, constant maneuvering, shields on 50% of the time, taking fire 33% of the time, 50% flux average, 67% weapon usage, no hull damage, for 167 seconds
Worst case, deplete fully in 45 seconds. In practice it would be near impossible to degrade this fast.
In this manner, CR depletion will still prevent a frigate from kiting indefinitely. Just using the ship puts an expiry date on the deployment. The more heavily its used, the faster this depletes, and heavily damaged vessels can't do anything other than hemorrhage CR.
A thought that takes this a step further...and what I wish CR would become
Spoiler
Larger ships can deploy indefinitely at current, they don't suffer from degradation, why?
What if there were a new stat, a CR replenishment rate.
Very low for frigates, very High for Battleships, yet not ever high enough that they can become immune to depletion.
A heavily damaged battleship, trading fire with its shields up and high flux
should suffer CR degredation
So if Destroyers replenish faster than frigates, and cruisers faster still, and battlecruisers even faster, and Battleships fastest of all, then they could at certain combat levels keep things up indefinitely. Yet if harassed long enough, or if their fight is close enough to a struggle just to survive, then they too will inevitably falter due to CR depletion.
Obviously CR beyond your campaign level shouldn't be achievable. if your max CR was 61%, then replenishment should not be able to get you more than that if you sit there and let it accumulate.
Some numbers?
Ship | thrust | maneuver | Shields | Weapons | Flux | Taking_fire | CR_Pool | Replenish | Depletion | | Refill_in | Deplete_in |
Frigate | 100% | 100% | 60% | 50% | 60% | 25% | 180s | 15% | 115.25% | | 1200s | 180s |
Destroyer | 100% | 100% | 70% | 50% | 64.5% | 50% | 240s | 25% | 125% | | 960s | 240s |
Cruiser | 100% | 100% | 100% | 60% | 75% | 70% | 360s | 45% | 144.5% | | 800s | 362s |
BattleCruiser | 100% | 100% | 100% | 60% | 90% | 75% | 420s | 60% | 160.25% | | 700s | 419s |
Battleship | 100% | 100% | 100% | 100% | 100% | 100% | 540s | 80% | 180% | | 675s | 540s |
Setup like that, only a battleship can hope to keep itself ticking endlessly, but if its that busy, it too has a best before sticker.
Consider that even active combat is typically a series of peaks and valleys for exertion, so every time your depletion falls below your replenishment you gain endurance. If your outnumbered, your shields, weapons, and average flux will likely be higher, resulting in shorter endurance.
The point?
Don't kite, you can't keep it up for long, and while maybe they can't either, if your kiting them, their pool is likely larger, and they can almost certainly do this longer than you can.
Don't be the unassailable shielded death machine that takes on whole fleets alone unless your a battleship, you can't keep that up indefinitely, especially once you take some damage, will you last long enough or get caught with depleted CR?