The complaints about the FBI have nothing to do with Meuller. Rather, they have to do with felony misrepresentations to the FISA courts over fraudulent warrant requests for surveillance.
"nothing to do with Meuller" is simply not true. You don't have to guess here, Trump is very open in communicating his mistaken belief that memo would kill the investigation. As such, it doesn't really matter what it is, trying to address it is tainted by corrupt intent.
Sure, FISA shouldn't exist. I hope you understand that Trump isn't trying to clamp down on FISA.