There is one thing that bothers me here though.
> Promotions don’t unlock new responsibilities; the new responsibilities and increased scope come first and then we recognize it with a promotion.
To some extent I agree with this. The part where I don't agree with this principle is that it's essentially saying "do the job of position XYZ, and after you prove to us that you can do it, we will recognize and pay you for it."
If people are taking on additional responsibility and having a bigger impact, pay them for it. Maybe Square does, but normally comp+promotion go together and so I'd be interested to hear evidence to the contrary. If someone has been operating at a level for 6 months, then why not retropay them for 6 months at their new salary? :)