> I wonder how much of the stuff he has said about Raptor is BS?

As far as I can tell, it's mostly true. The last quote in comment #166 does not tell the real order of events, though. In reality, the project first switched ISA from RISC-V to Power and only then was approached by Raptor. So, Raptor expressing interest was not the reason for the ISA switch, but the ISA switch was the reason for Raptor expressing interest.

> if the chip is only suited to replacing a system monitoring processor,
> is it that good?

First and foremost, this chip is about being fully open, and only then about being "good" (whatever that means in particular) :-)
The use as a board management controller for Raptor is just an initial use case for the SoC, if it happens. This doesn't mean the chip is only suited to this end. The original specs lacked some features required for a management controller. They were added to the specs at Raptor's request. The presentation description linked to in comment #168 doesn't even mention anything about management controllers or service/monitoring processors, but "tablets, smartphones, chromebooks and more".