I stopped drinking Coke for some years and now it tastes terrible, like gross sickly medicine. I don't think Coke changed its flavour all that much, I think that I appraised it more objectively and found it severely lacking.
If you stop drinking all the soda (fake or real sugar) your brain rewires to baseline eventually. And at baseline sodas are disgustingly sickeningly sweet.
This happened to me too. I don't drink sodas but in the very rare occasion there is nothing else I try to pick the zero types, like the other user said, they feel less sweet and less medicine tasting.