But we really don't need much sugar.
No, but we do need some. I don't drink tea or coffee, so no added sugar there (hot drinks seem to have largely escaped the sugar banhammer). I mainly drink fizzy water, but I sometimes like to add a dash of cordial to it. At the moment, I buy Rocks, which is much more expensive, but a bottle lasts me a couple of months, so I don't mind.
I'm not even saying that naturally sweetened drinks shouldn't have a sugar tax on them - just asking that they still be freely available for those who don't want sweeteners that they hate the taste of and find make them ill.
I do not believe that manufacturers are responding to consumer wishes by adding sweetener to their supposedly 'traditional' drinks: it's just that the sugar tax has made their ingredients more expensive, so they're banking on people not noticing when they bulk it out with cheaper ingredients (i.e. AS).
Artificial sweeteners are also very bad for people's health. Unlike sugar, we don't need any quantity of them in our diets at all; so if anything, maybe they should also have a heavy tax on them and the default for soft drinks be for them not to taste sweet at all. If people find that unpalatable, why should only one 'unhealthy' sweetening option be condoned and the other condemned?