What this means is that even if a malicious app manages to get root (or whatever) access due to a vulnerability it can’t make that persist across reboots
dm-verity within AVB protects the system and vendor partitions, but the malicious app on data can regain root anytime some of its code is triggered if the device is still vulnerable. The example mediatek exploit posted would elevate to root on a -user build too if you have an app calling the described ioctls. There are benefits sure, just being nuanced. A re-locked bootloader is only possible on a subset of devices. Enabling encryption on userdata should be prominently advised for though to have an evenings time to cycle credentials if the phone parts ways and assess fallout.
I dug up some links recently on userdebug (more for App compatability than security, no more “rooted device” complaining because of ro.debuggable) at App called mitID keeps saying my device is rooted - #6 by tcecyk - I’m sure the /e/ devs will gradually introduce those for devices time permitting.