"No one has ever achieved consistency as a screenwriter."

Really? What about John August? Steward Beattie? Rosenberg? Ted & Terry? The Nolans?

"No one has ever achieved consistency as a screenwriter" is more of a statement about the collaborative nature of filmmaking than about screenwriting.

You could write 10 consistently great scripts, but they all go to different directors, producers, actors, key grips, etc. The more elements that stay the same, the more consistency you get.

I don't know about Stuart Beattie and the Nolans, but I know John August has written duds that never went anywhere and I think some of his produced credits have to be considered duds. I know Rosenberg has a slew of duds that will never see the light of day. I remember that once his new agent had to pour through twenty of his scripts and most of them sucked. Ted and Terry would tell you themselves they've written duds, though it could be argued that the ones that made it into production have all been good (so, maybe, they're consistent).
I think it's hard to argue that any writer consistently writes great material. Anyway, just another opinion, fwiw.

I agree with numbers 1 through 10, although I don't care about 6 and 7 much. I really enjoyed Hare's "Plenty" and "My Zinc Bed", although "Damage" was just okay.

"Never take advice from anyone with no investment in the outcome."

Interesting. What would one define as "investment in the outcome?"