I don't think 'crutch' is fair. It seems like the clear way the rule is supposed to function.
However, I don't want to drag this too far off-topic, so I went ahead and talked about the 'gimmick' thing over here,
so we can keep the conversation in this thread limited to the Haemonculus Covens formations.
I agree that there are plenty of occasions where we don't play by RAW (In the last BA Codex, the Sanguine Sword power lasted all game once activated. If you are shot out of a destroyed--not explode-- Assault Vehicle, you are allowed to charge in your opponent's assault phase. Master of Ambush lets you give Infiltrate to an enemy unit/character. The list goes on...) in favor of a clear RAI.
However, in this case, (Freakish Spectacle) the RAI seem perfectly clear. I know GW occasionally --lol, often--writes a bad rule, but this one seems pretty cut-and-dried. It seems very clearly designed to dovetail with Fear, which virtually all the HC units have by the time they're in assault anyway.
I have encountered TOs who made rulings that were closer to wish-listing, (usually in regards to Gate of Infinity) and I sincerely hope that doesn't happen to people. It does bring up a good point, however: if you have any areas of your codex that are rules of contention in online debates, it's probably wise to ask your TO ahead of time about it.
EDIT: If the tone of this comes off as aggressive or stand-offish, that isn't the intent! I like the relative non-aggression of these boards (or at least the threads I participate in on them) and don't want to piss in the sandbox by any means.