RCS does not go through Google servers. It is a standard offered by the carriers and gies through their networks, just like SMS/MMS.
Googles implementation of rcs does go through a google server and is incompatible with the carriers version of rcs.
is a fragmented mess after google forked it with their proprietary non-open version.
SMS/mms is a standard adopted by the gsma, rcs is not. Rcs was developed around 2008, it failed globally around 2015.