If you are thinking of the battle of Telamon, that was a raid, not a migration.
I don't think the EB team is against the horde option itself, but against the mechanism that spawns a huge army regardless of the strength of the faction prior to being forced out. Also, migration of a tribe generally occurred when it was displaced, not when it simply was conquered. Roman conquests did not cause hordes, yet in BI a faction will always form a horde when defeated. If this mechanism is different in M2:TW, I am sure the team is considering it.
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