Brain is much slower than expected

[Peanutbutter1]

I would suggest starting with reading this: https://hashcat.net/forum/thread-7903.html (most importantly the section "Major Feature: The hashcat brain").

of course the brain is most efficient and I would say sometimes only needed/meaninful for slow hash types (sometimes even the amount of hashes/salts is important too).
the brain has several features/settings to tune it see hashcat --help (most importantly the Brain Client Features, --brain-client-features).

It could make a lot of sense to avoid double work and to use several connected clients at the same time, also to avoid running the same password candidates/attacks again and again.

You could test with several bcrypt hashes etc and you will see that the brain is very clever and skips already done attacks and password candidates and therefore making the cracking much faster if you use it correctly (and how it was intended).
There are also some other forum posts that address speed problems or misconceptions.

Also make sure to use the latest hashcat version and/or the beta version from https://hashcat.net/beta/

Trying it on bcrypt hashes, I see that it does not offer any speed increases. On --brain-client-features=1 or 3, I see that the speed actually drops even though about 99 percent of the candidates are rejected. Using --brain-client-features=2, the speed remains the same but there are no candidates rejected, even after running the same attack parameters again on the same left list. Why does it not show rejected candidates for features=2? Thanks