wow, you need some architectural discipline there. Postgres and mysql: what was the reasoning behind that?

We've acquired many companies over the years.

Ok that makes sense to me.

Post mergers the mantra is "you say that we will get $n from putting all our systems together and it will cost $n/10 but I say you are a bloody liar and want proof and hostages."

"Clump soul" https://en.wikipedia.org/wiki/Katamari_Damacy

ROFL.

Sorry, but this story is true in every Fortune 1000, except maybe a very small number of technology companies.

Why? Line of business team X demands product Y, that only runs on prem on DB Z. Done.

Nope. It's true of every Fortune 1000 who are poor at IT and in the hands of vendors. It's not true where I work, and I am pretty sure it's not true at Microsoft, Google, Facebook...