How about a little humility? You have no idea who else has similar problems out there. I'm sure Percona and other DB consulting companies would tell you otherwise, as would PlanetScale. (If this weren't true, they wouldn't be viable businesses.)
> github is a 14 year old company, with annual revenue in the hundreds of millions USD
You're making the classic mistake of thinking that having money means you can just wave your hand and hire whoever you want with whatever talent you need to solve your problems. The world just doesn't work that way.
As for the "hand-wavy" excuses, well, the people who know the issues don't need to disclose the dirty details in a public forum, nor are they often able to because of NDAs and other legal encumbrances. And it can be a career-limiting move to throw your colleagues under the bus.
You can choose to assume people are incompetent, or instead choose to assume that people are working as best they can under the constraints placed on them. I think it's better to assume the latter.