I’d say historically (modern history) you didn’t see any athletes eating ketogenic diets, but more and more you are seeing athletes (especially endurance athletes) eating Keto diets. Keto is great for aerobic activity, the idea of a tribe of early man persistence hunting a mammoth for example would have performed better long term in ketosis having unlimited stores of fuel (fat) rather than draining their glucose in 8 or so miles and “hitting a wall”.

It’s anerobic activity (sprinting or bodybuilding/Olympic lifting) where there may be a slight detriment in performance.

I’ve run marathons in both ketosis and running on glucose. I won’t go there because it’s anecdotal but marathoners, body builders and Olympic style lifters are not the norm and have different requirements especially competing for records. No doubt it’s one thing to live in a natural state of ketosis and treat yourself to a performance boost with some fruit when you are about to burn any glucose than what almost the entire modern world does and spikes their insulin levels all day every day and their body/cells basically not even familiar with how to use ketones as a fuel.