Hotline...
The semi-main at the panel is not needed at all.
OCP occurs at the MAIN -- which is 100 Amp.
HI is out of his depth.
It sounds like some one over the years needed more branch circuits and installed a standard 200A off-the-shelf panel. In which case the breaker came as part of the deal.
I see these all the time in the Big Box.
My come back to the HI is that I don't need ANY C/B in this situation, but that makes for a quicker cleaner installation... and the HO has an additional OFF switch.
Down the road, the HO could have the SERVICE upgraded to 200A and bump up his panel feeder to equal the Poco's Service Drop/Service Lateral.
