People talk about "controlling for other factors" when discussing associations all the time, even in non-technical press coverage. They are talking about (a).

True, true. "Gold standard" or "preferred level of evidence" versus "what's mostly conducted given the funding limitations". However, to make it into a guideline, there are often RCT follow-ups for hopeful associations uncovered by the lesser study designs.

look for the keywords "g-formula", "g-estimation", "inverse probability weighting," "propensity score", "marginal structural models," "structural nested models", "covariate adjustment," "back-door criterion", etc. etc.

I, of course, know all of those. The letters, I mean.