That's what a clean install is, yes. I find in-place upgrades or CPUSE "clean-install" (which is very much NOT a clean install) on management servers to be wastes of time. Almost all of my management servers are VMs because Check Point's branded management servers are wildly overpriced and underpowered (spinning disks were the default for waaaay too long). It's really fast to reinstall the OS on a VM on decently modern hardware.
You need to upgrade the primary first, otherwise the secondary can't sync to it. I don't see much point to wiping and rebuilding the secondary, syncing to it, promoting it to primary, wiping and rebuilding the primary a second time, syncing to it, then promoting it back to primary. All the steps in italics seem unnecessary.