Agreed on zero being better than diet. They actually use the same sweeteners, but a different flavor profile.
FWIW, in the US at least, Pepsi Max also became Pepsi Zero.
I suspect both are getting away from the 'diet' moniker because of the fact that people not on an active weight loss diet prefer them, ruining the played out joke of 'haha he ordered 2 burgers and a diet coke.'
Turns out Diet Coke is actually a different drink. When they made it way back when with the previous genesis artificial sugars it tasted terrible. So they actually re-created the recipe for the fake sugar.
Coke Zero is the same as Coke but with newer generation Artifical sweeteners. That’s why many who like Coke end up not liking Diet but like Zero much better.
My wife had never tried Coke Zero before we met and she also prefers it now.
Not sure what they use in these alternatives but Diet Coke/Pepsi taste pretty bad so it must be a starkly different artificial sweetener.