Has anyone else started a new job with the promise of interesting work, just to end up spending all their time writing e2e tests for crap code written 5 years ago by a contractor who clearly couldn't give 2 shits?

Every job comes with such promise, else they wouldn't find people :P Did not really happen to me, I was the outsourcer making the initial crap that flew away when the maintenance had to be done. They'll find some cheaper internal person for that :P Nah, i also did heavy maintenance at some company. It was fine.

Short answer is: NOPE!

I had 5 years in c++ high performance data analysis. Was told I'd be doing similar stuff for genetics. First month I was dumped on html bullshit (I'd never written any before).

If they are paying you to not work on money making parts of the product, they're either really big, something bad happened recently or you're not charging enough. That's the most common reason that they don't happen + if you want good quality, it needs to be tested by humans regardless.

TLDR: The previous contractor didn't care because the client didn't care

Yeah, I've worked job where the most interesting part was the fucking FizzBuzz test I had to do