Few comments :
1) Best to say how (in Windows) to defrag disks by right clicking on the disk in computer, and looking in tools tab. Rather than assume it's obvious, all to many Win users don't ever seem to do it.
2) Some of the GRUB explanation may be misleading with newer installer versions.
There's a thread, discussing boot and / partitions, and a pointer to the Wiki page here, where the leader of the YaST team explains current thinking.
XFS Boot problem
The 'active' partition is used by the Generic boot code, which is likely to be installed in the MBR (or is already present). Then GRUB would get installed in the superblock of ext2/3 filesystem in a partition.
My understanding is, that installing 'GRUB' in the MBR is discouraged when Windows is around due to issues with it being overwritten by 'doze, or possibly causing some scare, when a security utility sees a change.