I know i skipped 8 and 9 and sar at one point was no ramdisk in boot which made rooting challenging. I remember downloading firmware where there was boot, recovery, system, vendor, product etc at one point but never owned those early sar devices yet only read documentation about it. From what i am seeing now, super is a game changer from what it seems and also brings back some tradition of android (sorta lol) which is ramdisk in boot. I agree that these rapid changes google does can be quite to understand. I guess the question i should ask what version of sar is my device or 2020-2021 devices? Lol.Sorta.. they arent mounted during flash.. super.img is flashed then logical partitons are mounted on each boot.. and yes.. they are labeled as dm devices when device is booted up.. it is called dynamic or logical partitions
and yes, system is not as picky as say vendor is and I am aware devices use system as root. you can read up on google about it lol.. theres other ways to edit it than mounting the dm devices such as making a modified super img or using fastbootd or even twrp etc.