If your phone's manufacturer disabled the necessary power saving settings, I doubt they'll enable them for the Android 15 terminal.
To be fair, for every well behaved background app (ie. a ssh server that's listening on a socket, which should consume basically zero power), there's probably 10 other misbehaving app that's phoning home every 30 seconds for ad/tracking/analytics purposes. Moreover, "battery life" is a metric that often shows up on reviews, so it makes sense to game this metric as hard as possible, especially since most people probably aren't running servers 24/7 on their phones.
I run into issues with the smart watch integration app getting killed before Google Maps, even when I'm not navigating on one of my devices. No way to whitelist the integration app or set some kind of preference, it's just a lottery, probably based on guesstimated power consumption (which, for an app with a Bluetooth lock, will probably be above average) that I want to tweak.
When these are the tasks that are killed, it costs me more than whatever precious bodily fluids that some ad/tracking/analytics stuff may sap: It costs me real money.
Dollars I have lost due to things phoning home against my expectations: Close to zero -- if not literally zero. (And close to zero time spent managing that.)
Dollars I have lost due to things failing to phone home when I want them to do so: More than zero. (And hours and hours of time spent trying to make them work more reliably.)
None of this invalidates your use case, but given the rarity of your use case compared to the more common use case, I hope you understand why companies are implementing it not purely out of "spite".
A thing can be abhorrent and disdainful and motivated by the best and most pure of intentions, all at the same time. These are not in any way mutually-exclusive constructs.
Rarity?
Perhaps the best way to make sure a thing remains rare or unusual is to neuter it straight out of the gate. In the past few days here we've seen SSH servers and Docker containers on Android, with the repeated caveat of "Yeah, but the task killer won't let that really work." And that's absolutely true: It won't.
Don't forget all the crap they can run in the freed capacity now!