I'm open to be persuaded, but initial impression is a lot of bullshit there.

The main finding from an admittedly quick look is that drinking artificially sweet soda may encourage people to eat more calories and gain weight. If you're controlling your calorie intake then that's irrelevant.

Outside of that other claims seem highly questionable.

I push back a little on this, because most of the time I've heard people say diet soda is as bad or worse than regular it's because of unsubstantiated woo. Is drinking only water better for you? I'd guess almost certainly.

Is diet soda particularly harmful? I doubt it - and it's almost certainly better than regular soda (or all of those high sugar fancy juices). It can also be really helpful when losing a lot of weight as a zero calorie snack.