Ok, it doesn't really matter as on a pixel device your data should be getting backed up and 1 slot should have a working boot if you are switching a & b on system/security updates. (Besides the google gaffe of the android 13 update of needing both slots updated). I liked custom recoveries, but they aren't really necessary, and on newer devices not feasible at this point. I wasn't disagreeing with you, but as stated also above there are other options to backup things and you should always have a working slot to boot.I think you mean slot. It's important to understand that each CRITICAL partition has two slots - bootloader_a, bootloader_b; boot_a, boot_b; system_a, system_b. However, the /data partition has only one slot. This is why it is not possible to "dual boot" on A/B devices.
My point was that while making nandroid backups with TWRP is pretty convenient, it should also be possible to dump the partitions of a slot via ADB without using TWRP.
Additionally, it's not the A/B layout itself that makes custom recovery difficult; it's the fact that most A/B devices do not have a bespoke /recovery partition; instead, the recovery kernel is in the boot image, alongside the system kernel. This normally isn't a problem, as installing TWRP (the right way, by patching the boot image) replaces the recovery kernel with TWRP; the problem is, since Magisk also patches the boot image, it seems the two do not play well together. I have been unable to install both TWRP and Magisk; this results in a boot loop.
Therefore, I maintain that the best way to use TWRP is via live booting, and it should not be installed..