There is a line missing in the Firebeetle bp that should make it work properly:

UnitBlueprint {

Merge = true,

There is this line in my mod and it works.

Also, I did a mistake for the Ilshavoh small speed buff. It's supposed to get +0.2, but the base is 2.5 (not 2.6) so the speed should be 2.7 (not 2.8).