I already have a GSI running on a device, which was flashed onto a stock ROM (pie in this case), after wiping the data partition (in TWRP) and erasing the stock system (using fastboot erase system).
It seems logical to me that I can then install a different GSI (e.g. the new Android 10 (Q) eOS GSI) if I first wipe the data partition again (using TWRP) and then erase the GSI (using fastboot erase system).
Am I wrong? Is there some reason that I don’t know about why a GSI must always be flashed onto a Stock ROM?