I don't believe the only issue with the phones is aggressive battery throttling. But, it is one of the most problematic. For what it is worth, it is not just the Hubitat app that you have to be concerned with. For instance, on Android, almost all apps that use geofencing rely on Google Play services for the location monitoring. So, in addition to the app in question, such as Hubitat, Ecobee, Smartthings, or whatever you are trying to keep alive for geofencing, you ALSO have to find a way to keep Google Play Services up and running all the time.
As I said before, I did a bit of research on this when I had issues back in the ST era. At the same time, I was having geofencing reliability issues with every app I was trying to use my phone for geofencing with. This includes Smartthings, Ecobee, IFTTT, and Life 360.
In addition to the aggressive battery situation, I also found out that using a magnet anywhere near your phone (Like the cases that have magnetic closures and those popular magnetic mounts systems) will cause your compass calibration almost instantly degrade. Guess what? Google play services requires your compass to be somewhat accurate to get a proper location (I don't know why, but it is what it is). I did not know right away what was causing the compass issue. But, I had read about an app called GPS info that would allow you to keep GPS alive and give you a visual indication of the compass calibration (red/yellow/green). Using that, you could do the magic figure 8's that recalibrate your compass. There are several sites that stated you could do this with 3 or 4 figure 8's. That turns out to not be true for a compass that has been screwed by a magnet. I would spend upwards of 5-10 minutes fixing my compass calibration. That is when I researched to find that the magnets were the cause. I was having to do this 2-3 times a week. Everytime I got home and did not see myself as present, I would check, and sure enough, 9 out of ten times, the calibration of my compass was off.
Interestingly, I found that staying away from magnet cases and mounts has left my phone in a state that I have not needed to calibrate my compass but once or twice in the two years since I discovered. Fixing, or at least understanding the aggressive battery issues by removing Hubitat, Google play services, and the GPS Info App from battery optimization and putting them in never sleeping apps has left my phone reliable until two Android updates ago. Then, I figured out how to pin Hubitat to the most recent apps. So, that has at least temporarily fixed it for now.
What this came down to was that I was blaming: Ecobee, IFTTT, Smartthings, Life 360, and other apps for something that my phone was doing wrong 99% of the time. If it were just Hubitat, then that would point to an app problem, but all it takes is a simple Google search to find that nearly every app that uses geofencing has issues and the vast majority boil down to the phone aggressively killing services or problems with the phones location services.
So, while I share your frustration, I don't think it is an issue that Hubitat can solve for us unless they can come up with a way to prevent phone OS's from killing our apps and fix everyone's varying issues with their specific issues with location services in general.
So, since I need something that work, I use Hubitat native which works 99% of the time now that I have dealt with most of the phone issues. As a backup, I use a tasker profile to push an update to my presence sensor if my phone misses. That fixes the majority of the other 1%. On the rare (once every 3-6 months) occasion that both of the former methods fail to work immediately, I have a dashboard that I can just open and toggle.
Other Apps with Geofencing Issues - short list
Arlo
Solved: Arlo Geofencing not working correctly when using ... - Arlo Community
Ecobee
https://www.reddit.com/r/ecobee/comments/lx4ztj/ecobee_smart_geofencing_doesnt_work_as_advertised/
Life 360
Why Does Life360 Show the Wrong Location?
Smartthings
ST Geofencing problem Android 13! - Android - SmartThings Community