I tried to google a benchmark of ext4 + LVM2 thin vs btrfs. The closest that I can find is a 2015 benchmark…
In 2015, a PostgreSQL benchmark shows ext4 + LVM thin is far better than btrfs:
2022 march benchmark in Qubes OS’s issue #7300
Hmm. What does that benchmark actually mean? btrfs seems better in the benchmark. But that is not normal because Qubes OS doesn't use direct I/O for the pools that use loop device (described in issue #7332)