Since as a conjunction can refer both to causation and to the passage of time […], and the mavens believed strongly that since there's potential confusion over which meaning of since is meant, one should avoid since as a causal conjunction.
I agree with you 100%. Language shifts and changes over time. Sometimes in beautiful / useful ways and sometimes in ugly / detrimental ways (losing a word that was the only word that meant the thing that it meant for instance)
If it changes based on how people use it, then why not use it in the way that you want to see it evolve. Maybe even advocate for it to evolve in the way that you see as beautiful / useful if it's that meaningful to you.
For example, I love that we verbify stuff more these days. That's super cool. I do it all the time because I love that active voice. On the other hand flammable and inflammable slowly becoming the same thing kinda sucks because now what word do you use when you want to say what "inflammable" used to mean? You can do it. Just not as nicely. If people evolve the language that way then fine, I'll go along. But if language naturally changes based on usage, what's wrong with using it the way that you want to see it become (or remain)?
(...) the mavens believed strongly that since there’s potential confusion over which meaning of since is meant, one should avoid since as a causal conjunction.