Well the thing about evasion skill is that it's the easy one of the defensive skills - you have a skillup chance when you evade *or* when you get hit, including getting hit from 0 due to Stoneskin or something. Dunno if you can skillup when you blink damage (with blink/utsu).
To skillup parry, guard, or shield, it actually has to kick in. This isn't too bad for shield, since shield kicks in pretty often if you use a small shield. But parry is unpleasant and guard is just plain painful.
Anyway, here's the general rule for skillups (not applicable to things you can skillup by casting on yourself or other players): the enemy you're using must be Even Match or stronger in order to cap your skill. If it's 1 level below you, it'll take your skill to whatever it capped at, 1 level ago (i.e. when it was EM). If it's 10 levels below you, it'll take your skill to whatever it capped at, 10 levels ago. And so on. The actual number it'll take you to, varies by how good you are with the skill.
This makes low-rated not only cap lower, but also be harder to skillup. Say you're trying to get your last point on a D skill (caps at 210 at 75) compared to an A skill (caps at 276 at 75), for some melee skill or other. (What I call A, some other people call A+, just a matter of semantics.) Either way you've got to hit that friendly EM+ mob. But the person with D is hitting it with 209 skill trying to get to 210, and the person with A is hitting it with 275 skill trying to get to 276.
Needless to say, the person with 275 skill is gonna be hitting more accurately (and is more likely to hit for more than 0 which is also a requirement, although it's generally not an issue) than the person with 209 skill. They have a 66 point lead, which is quite a bit. This shows up even more painfully if you don't skillup on EM, but instead go skillup on T-VT.
Also note another consequence of this - someone with A skill can hit 210 on a level 62 mob, because level 62 is when A can reach 210 (212, actually). Someone with D skill has to use a level 75 mob though. Which makes organizing skillups by the actual *skill level* somewhat impractical, unless everyone has similar rankings in their skills. Because "skilling up to 200" to one person may mean Kuftal Robber Crabs while to another person it may mean Boyahda Steelshells.
I don't know whether or not the *chance* of skillup on any given hit is worse for A skill compared to D skill or something. I wouldn't be surprised if it were, but it might not be.