If we're getting into that sort of language - I don't even run Incubi competitively anymore and think they're a point sink we don't need.
That said, the point still remains, if you run anywhere between 4-9 Incubi, what serves them better? No HQ, a Haem, or an Archon?
I still think the answer is Archon regardless. Yes, maybe the unit becomes so expensive it is a giant target - such is the life of Incubi, ruddy 4 Incubi with no HQ attached (despite how useless they are) will be a target of likely high priority from almost any opponent who fears assault. If the opponent does not fear assault then 8 Incubi+Archon+Haem will draw as much fire as 4 Incubi.
Yes, you can have a shooting army do the job of the Incubi.
Yes, you can use Wyches or Wracks, or Beasts, or Hellions as your assault tool instead of Incubi.
But if you field Incubi, how do you maximize Incubi and make them best able to be useful to your army?
I don't think the answer is 'with no HQ' because those Incubi are gimped and unable to do a lot of things for your army. You are paying for an elite assault unit and then agreeing that there are a lot of targets you won't even assault because your elite assault unit can't handle them.
I think they work with a Haem, but all he does is make them moderately tougher to kill.
I think they combo very well with an Archon, whose strengths emulate theirs, who has some abilities that lessen their weaknesses to a large degree, who opens them up tactically, and who will want to assault the same sort of targets they will want to assault.
That's why I think the Archon is, by a large amount, the best combo with Incubi. Haems can work, but aren't as good, and the best is to have both (as either getting FNP or FC onto Incubi is a good thing)