Did you noticed.......

[Pocus]

what bother me a bit (well more than a bit) is now that blood magic is much more restricted to native blood nations, then SC will concentrate into these nations.

Whereas, as a worst case, you could at least try to counter/temper the influence of SC (which are mostly blood creatures) in doms I by starting blood magic yourself (I remember a pbem game where after 15 turns of efforts, starting from nothing, I produced one ice devil every two turns with a mystic which was empowered in blood magic).

But this was a very poor workaround. What would have been better is to reduce much further the nastiness of big creatures in Doms II (several mechanisms can be found to increase how a sole creature can be mobbed by several smaller ones). With more than 12-15 demons prince available, there is in practice no reduction in the numbers of SC dominions games will see, with the annoying change that they will be controlled by the 4/5 blood nations.