Probably better than sugar on one dimension, still genuinely contested on another.
Artificial and non-nutritive sweeteners (aspartame, sucralose, stevia, monk fruit and others) are a genuinely contested area — marketed as an inflammation-friendly sugar substitute, while facing their own set of research questions.
Swapping added sugar for a non-nutritive sweetener avoids the blood sugar spikes tied to sugar's inflammatory effects — for someone replacing regular soda with a diet version, that swap is generally a reasonable one on this dimension alone.
Research on artificial sweeteners and the gut microbiome has produced mixed findings — some studies suggest certain sweeteners may alter gut bacteria composition, though results vary by sweetener type and aren't fully consistent across studies. This remains an active, evolving research area rather than a settled question in either direction.
We don't treat artificial sweeteners as equivalent to added sugar (the blood-sugar case for switching is real), but we also don't treat them as a free pass — the honest answer is "probably better than sugar for this specific signal, still an open question on others."
If you're drinking diet soda by the litre hoping it's health food, the bigger opportunity is probably just drinking more water — not the sweetener debate itself.