Yeah, ended up building a new vCenter on 7.0 U2d and using Advanced Cross vCenter vMotion, and rebuilding all my hosts back to ESXi 7.0 U2c.
A complete and utter pain in the arse to be honest, but better safe than sorry since I am running a number of 2-Node vSAN clusters in various branch offices I can't get to. I still have my older ESXi 6.7 hosts that I can use as swing hosts to prevent downtime, but dang this blows.