I'll preface this saying its mostly anecdotal, but I'm a diet-soda drinker. I remember reading(somewhere, memory fails me) about the actual sweetness taste itself may cause a hunger response(body tastes sweetness, releases chemicals to breakdown/absorb sweetness, finds nothing/something different).
I'll say from personal experience this is something I noticed this long before I read anything about it. I tend to eat 2 meals a day(1 small/medium and 1 large meal a day, and small snacks sandwiched around workouts on those days), so I tend to have fairly large gaps(compared to most) between meals some days.
If I drink mostly water or unsweetened tea throughout the day, the water makes me feel fairly full and I don't really "crave" that next meal.
If I drink mostly diet soda, by later in the day I am very noticeably hungry, the more I drink the hungrier I seem to be.
So well I agree that there isn't enough data to really draw the link to diet soda and making you fatter, as someone who inadvertently tests this hypothesis many times(granted, being only one person), it seems rather obvious to me that there's at least something else going on, be in the sweetness, or some other process.
I think where we'd both agree is that if you eat X calories + diet soda consistently, you're not going to gain any more weight than X calories + water. But if the one is influencing your hunger levels, you will probably won't be as likely to stick to that regime as a result, leading you into the trap of over-rationalizing the calorie savings of the diet soda(giving you a double penalty, if you're feeling hungry you will take any excuse to rationalize eating more, that's human behavior).
You specifically say the satiety between artificial vs real sweeteners, but what's your opinion on artificial sweeteners vs no sweeteners at all? Since that's the real comparison, since for a lot of these "dieters" the soda is a water replacement, not a soda replacement.