Maybe the novels explain it differently, but that isn't at all how the series presents itself. Not even remotely.
Kirito explained to noob-master-Klein that skills auto-activate once you think hard enough about them. The "input motion" isn't as if you perform the Crimson-Leaves Strike from "The Book of Five Rings," there was clearly no skill involved. You put your arm in the approximately correct position and it works when you think about it hard enough. This barely registers as Dragon Punch input difficulty.
Klein wasn't exactly skilled at martial combat before. He started Sword Art Online just coming off other MMOs, the regular kind. Once Kirito told him how to do it, he was fine, and now he's one of lead parties. You think either of the two girls knew any manner of martial combat before? Sachi was in a computer club and the other is just some random girl who likes cute things, no reason for her to even try SAO in the first place was given. They didn't have that much difficulty. Sachi was only having trouble because her guild forced her to switch to front-line defender, and given the very real threat of death in that group position, it's understandable. Sachi's friends had no trouble at all pulling off skills.
Knowing Kendo (allegedly) doesn't help Kirito more than giving him a little experience in moving his arms in specific ways to avoid any ambiguity on the skill initial position command. Maybe it makes for pulling off strings of commands faster. Over time, that's the same for anyone with any game in any genre.
Aside from the input method of holding your arm in position or making an upward swing from low (to bat aside the boss' weapon) instead of a horizontal swing (to simply attack) as clearly seen in episode 2, SAO isn't any different from TERA. They use timing here for extra damage, the same way that most MMOs use temporary skill debuffs that combo by other party members' attacks. TERA does that. Guild Wars 2 will be doing that too. The timing is just more precise...and that isn't any different from any console action-RPG where lag isn't an issue.