Earlier quoted context omitted.
He climbs all these routes with a rope dozens to hundreds of times before free soloing them. The routes that he free soloes are also considered relatively easy to intermediate in skill level, well within his skill level. The really incredible part of his free soloes is just how long his body can last. It's Olympic levels of endurance.
Is his free solo climb of El Capitan considered an easy to intermediate route?
“Requires considerable knowledge of ropework, knots, and protection to climb. Although "free-soloing", or climbing without a rope, is admired and even revered by some as the purest form of climbing, it is a rare sort of person that enjoys climbing significant class 5 pitches without a rope.”
Class 5 is subdivided in 5.1 through 5.15, with ¿some/each? having a further a through d rating.
The route he took is rated 5.12d, maybe 5.13a (https://news.ycombinator.com/item?id=14500208), so that’s highly elite. Free-soloing is easier than soling with safety ropes in the sense that you won’t have to haul up gear :-) but of course a lot harder mentally.
I think ratings ignore length of the climb, and that matters, especially in this case, where there’s little to no time to rest.
You have to be confident that you’ll be physically and mentally fit enough for the entire thing (climbing down is more difficult, so you’re committing going all the way fairly soon). For Honnold, that meant almost four hours.