If it's just average then tell them that your open source project is proof of your technical abilities, you're happy to do culture / leadership conversations and answer code-review style questions about the technical design of your projects, but that otherwise you're not interested in passing an arbitrary leetcode bar.
OTOH, if you get an offer and you feel queasy about things, you can have the all-too-rare-in-life privilege of asking impolite questions and maybe getting a real response, e.g., "The way you made me jump through all these hoops makes me think that the company culture might be rigid and dysfunctional. Is it?" And then see what happens!
BUT, i have no idea if they're willing to agree or would just drop me after that altogether
If you're completely breaking the process, it may harm that, leaving you either:
* as a Senior / Principal that isn't actually ready for that kind of work in their specific area and their specific software type
* as a level 1 or 2 that absolutely could be a Senior / Principal and now you're going to have to crawl through their ranks slowly.