Khang played a deck with only one Birdface. So it isn´t that essential. Can you replace it? No. It's a deck thinner and you get
a key card. Do you need 3? In my eyes, no. 2x is enough but that's a personal preference.
Elaborate why 3x MW is a mistake? Not that I use that card, but I'm just curious.
First of all, yes I know what Birdface can do and its benefits in a harpie lady deck. Like I said, it isn't replaceable, but to add more than two of the same cards in a deck is not something I would do. I'd make some adjustments and throw in something unexpected just for a somewhat different gameplay.
But that's just me. Like you said, if you throw in 1, 2, 3 or even 0. Thats up to the creator himself.
Furthermore, Not throwing in a 3x MW because it's poppable is not a correct reason in my eyes. Most of those cards are. Heck even cards like Sergeant, Mirage etc. do a good job. Fact is, it's a staple and those can be used in any deck.