Anyhoo, I would say that 5 might turn out okay, but one problem I would have, is that this will drive people away from trying more off-beat party combinations. With 5 party size, 90% of people will be running generic party of tank, healer, caster, ranged damage and chanter for the auras.
Don't be so sure about that. I've finished the game on Hard without a Priest and limited use of scrolls, something that is apparently deemed very hard by most people. I even played some parts without Pallegina, so I had no healer whatsoever. There is also the fact that most people would be willing to experiment if only to experience the different companions.
6 out of the 8 companions were written by people no longer working on PoE, including 4 of the 5 most popular ones. The new writers wrote Verse and Kills-in-Shadow in Tyranny. I think most here who played that game know that's not very encouraging.
You're a liar. We only know of Paul Kirsch and Carrie Patel on PoE 2 and I'm sure they didn't write Kills-in-Shadow. A character I happen to like, a nice mix between Verse's "No shits given" attitude, her obvious respect for her duties as Bovark and a general concern for the survival of her race and culture.