Is robocop a robo-brain with a non-standard chasis?

Yes and no.

Yes they are both brains planted on a robot chassis but they differ on their role.

From my understanding, the role of a brain on a robobrain is to provide processing power for the robot. The brain will be wiped of its memory and programmed to do certain task/s.

There are exceptions with certain robobrains where they still act human but this is merely because they have not undergone the memory wipe.

Robocop on the other hand has a robot chassis that serves as a prosthesis for the brain. It will more or less function like any other human.

I guess the difference is the robobrain is programmable and robocop is not.

edit: typo

Yeah, at first, I guess Robocop and the Big MT bots are "just" a cyborgs, that just happen to have very little organic components remaining. Robobrains, yeah, are probably just typical robots with a meat-based processor added in.
Later on though, they start forcing all kinds of insane programming on robocop, trying to force computer code more and more to dictate his behavior. They might have been wishing they had a robobrain rather than a cyborg. But computers aren't really that good at certain kinds of thinking... so it led to...problems.