Sorry, I only skimmed this one. I recently read an article, sorry I don’t remember where, maybe Hamodia? that said that diet drinks increase the desire for sugar in ways that regular don’t.
Personally, in dealing with modest amounts of sugar subs, like one teaspoon, I’d sooner go for saccharine. When you’re talking soda, not sweetening your coffee, I think the amount is too high for me to feel comfortable with any substitute.
YMMV, don’t know your whole story.