> there's absolutely no evidence at all that it helps with weight loss

I didn't claim this. "Healthy" food is a subjective term, and to most people does not mean "something that makes you loose weight". Compared to non-diet pop, it is a healthy alternative.

If you're trying to loose weight, stick with water. If you are managing your weight fine and enjoy pop, diet is better than non-diet. The studies you linked to support this.

Diet soda does not cause weight gain.

Diet soda makes you hungrier, and that makes you eat more and gain weight.

Root cause vs. proximate cause. If artificial sweeteners prime the body to expect calories that it doesn't receive, and (or by some other mechanism) this causes later overeating, then it's fair to say that diet soda does cause weight gain.

As an aside, I have a hypothesis that naturally focusing on proximate vs. root causes is actually a big contributor to the divide between major segments of the population.

Control being pure water, unsweetened coffee or caffeine solution? Give me proper science.