The question is, would the work have been done sooner, or more effectively if they had just fixed the C++ code rather than spending a lot of time creating rust,

The question is, would the work have been done sooner, or more effectively if they had just fixed the C++ code rather than spending a lot of time creating rust, only to rewrite said code? I mean to this day (and i just tossed off a firefox build yesterday to see if most of what I was saying is still true), the firefox maintainers can't even be bothered to fix the tens of thousands of warnings that appear when built certain ways. That is a really low bar to cross with a C++ project, and they haven't even bothered. I've worked on projects where we had a recommended compiler, but we always spent some time assuring that the project appeared to work with the latest gcc/icc/whatever, because at some point those newer compilers would become the defaults, and also because they frequently pointed out issues in the code. Its just a cheap way to fix undefined behavior bugs. So, I think the only answer to that is yes, that long stretch before they dropped the rust code was wasted time/effort.