It's way late and seriously over budget, hard to call that a success.

It's an unconditional success no matter how you slice it.

What are you talking about? What is the budget? Was there ever a deadline? Who ever decided those?

~3 months start to finish and the price of 1 engineer for a year, to rewrite a critical infra codebase that tens of millions of user software relies on. Truly the goalposts keep moving. This kind of project would've have been 10x the effort and price a few years ago.