So just to make things clear here.
If this is not on top of LVM, this would mean your comparison of performance is actually comparing apples and oranges. This is not simply comparing ext4 and brtfs, but different pools, different partition scheme, different sector size and as you said in other thread, a whole rabbit hole to dig in. Still interested into digging that, but as for you, I do not have either the actual deep knowledge necessary to have deeper insights than the ones I dropped in my initial thread for sector size/alignments, where PR was created but didn’t patched an iso to test it on distinct laptop to see what would happen if LUKS+LVMs would be aligned and if and only then performance would be faster (it definitely should, since it makes no sense we use 512bytes sector size nowadays, where BRTFS is reported to not do that because of different volume management path used by Qubes to create volumes then passed to qubes to be used, hence different performance.)
To dig that down, I think it should again happen under https://forum.qubes-os.org/t/ssd-maximal-performance-native-sector-size-partition-alignment not here.
But yes: I think this thread is comparing oranges and apples, unfortunately.