Neither Coke nor Diet Coke are nutritious. Whether one or the other is a risk is specific to a person, and aspartame as well as other sweeteners aren’t fully understood in terms of risk.

I think these kind of simplistic statements serve to stoke fears around food than actually help people understand them. Added / excess sugar is associated to health risks but ultimately people need to understand their own health as individuals.

Here’s a Healthline article (by no means an authority but still fairly informative) to help expand.

https://www.healthline.com/health/food-nutrition/sugar-facts-scientific#8.-Going-on-a-low–or-no-sugar-diet-will-help-you-lose-weight.-