intensity is a subjective thing. what i consider moderate is intense to most people and extreme for obese individuals. what i consider extreme is something that resulted in terrible tendonitis around my chest and ankles, and sweat dripping in my eyeballs, pouring across my lips, a heart rate of 170-180, and a shirt so unpleasantly drenched i would often lose it
And I think it can be detrimental to mental states pushing yourself that hard too, it messes with opioid and dopamine circuits in a way that more moderate exercise doesn't
The benefits probably also apply more to depression and anxiety than anything else. I wouldn't expect exercise to "cure" ADHD, or anything axis I/II. But yes in moderation it's a great nootropic, and yes anyone at any level of achievement can benefit from better lifestyle choices like this.