> It's a lesson that's always learned far too late when it becomes slow and costly to deliver something new because you've amassed so much tech debt
No, it is just standard operating procedure: deprecate a working system and write a new system from scratch, with 50% of features not supported. This side-steps the tech debt and gives everybody artifacts for promotion. It screws all users of the system but who cares about them!
There are always two systems, one is deprecated and the other not feature complete.