When it comes to health, a paleo diet is perfectly sufficient but not necessary (unless you have strong intolerances to both grains and dairy).
In regards to sports performance, it is perfectly sufficient for strength/power sports. Endurance sports, you can possibly make it work with lots of yam consumption.
But is it optimal for any of these? I’m not sure if I would be surprised either way. One possible benefit is that a paleo diet is more nutrient dense than a diet that that includes grains, dairy and legumes. But the benefit of extra micronutrients compared to other diets is an emprical matter that has yet to be settled. From the perspective of volumizing, a paleo diet may be optimal.
Worst of all, they engage in too much philosophical (armchair) as opposed to empirical reasoning. While it’s true that the reason something is healthy or unhealthy for us is our evolution, it doesn’t follow, a priori, that just because X behavior occurred over evolution that it is healthy for us or that if X behavior did not occur it is unhealthy. This known as an appeal to nature. It could be the case that we evolved in such a way that a novel substance turns out to be accidentally good for us, or at least unharmful. A prime example of this is the benefit of moderate alcohol consumption.
Of course, paleo advocates do make empirical arguments. It’s not the purpose of this post to look at those arguments in detail, so I’ll only make some introductory comments.
(1) The randomized controlled trials thus far conducted haven’t been adequate enough to prove the superiority of the paleo diet.
(2) Paleo advocates talk a lot about gut physiology and the effect of grains, legumes, ect. This is still very preliminary work. Much of it is in vitro, so its hard to say if it will pan out.
With that said, let me reiterate that the paleo diet is a fine diet. If you choose to eat this way, nothing bad is going to happen to you. The question is whether or not staying away from grains, dairy, and legumes is worth it.