It is a success because it is a concrete milestone that shows the founders have fulfilled their roles to satisfaction. An exit is not the only success, you could also simply transition into being a successful private company, but then there's no clear finish line. Now it is clear, no can argue the founders success, it's written in black and white and made public for all to see, they achieved an undeniably great thing.

Customers are always a product for shareholders, that doesn't suddenly change when a company is sold to other shareholders. And anyway, it could be a good thing, obviously Etsy has great experience with taking care of their customers and their partners and with running a huge business. Who says anyone was abandoned?