Sometimes coincidences are just coincidences. Other times it's more than that.
An interesting question (I'm not sure about) is what is considered reasonable evidence in the field of toponymy. In general for etymologies I think what I've seen is that the most explanatory/plausible/consistent theory is generally accepted among existing theories. That is, the best current guess is tentatively accepted as correct, until additional information suggests otherwise. But it's really hard to be confident in something like this.
The problem is, as I said before, that there is no way to get a larger statistical sample than one: maybe it's etymology A, maybe it's etymology B, and there is (in general) no direct evidence for either, and if both are consistent with the data then no clear reason to reject one over the other, and most importantly, no way to check in the end if you're right or not-- because every etymology is independent. Unless you find patterns (like most cities in an area being named after rivers, which still isn't a "rule" just a trend), you can't support it.
A folk etymology is a good theory that has been shown to be wrong. Your plausible theories may be folk etymologies (yes, more technical, but still, appealing, plausible stories!) that have not yet been shown to be wrong. Or they might be right. I'm not sure how to tell.
So, no, resemblance is not evidence for (or against) a particular etymology. Your "therefore" (in the last post) is not logical-- more like "maybe". (Again, I'm not saying you're wrong, but I also don't know how to confidently show that you're right either.)