Six years? The first MBP with the butterfly keyboard was released exactly 3 years ago.

The (now discontinued) 12" Macbook was released in 2015 and used the butterfly keyboard first (it was also their first foray into USB-C).

It'd be interesting to hear how they went about determining the keyboard was solid enough to use in the Pros when it clearly wasn't, even 3 design iterations in and almost 5 years later.

Ah ok I’ve been waiting for a while to replace my 2013 MBP and no suitable replacements have been available since then. They probably designed the crappy keyboard a couple to a few years before shipping it so I’d still count that as time they’ve burned on this. But two or three years from the time outsiders discovered the problem should have been long enough. Aside from having other options in the pipeline they also had the old good designs to fall back on.