if we started from scratch today, we wouldn't choose to have it this way, but we started a different way before, and it's been a difficult path to get to where we want to be"

This is just how software development for a large public project goes. If you want to land big changes in a finite amount of time, you take the path that breaks the least number of things along the way.

Once the whole ecosystem is rust-based, they can always trim out some of the redundant intermediate representations for performance gains.