Is it true that only invokers can learn spells on low level mobs?

I've spammed things like fireball and such on low level mobs, to practice them, because if I only cast while leveling, I'd get to 38 still on the second tier of spells....

My question is...for classes like bards, necros, druids, shamans...that have cast/commune/song options that are really important to competing in pk, are they incapable of learning while not ranking by casting on loads of lower level mobs like invokers can?

So as a bard you can just spam songs like an invoker spams spells in some out of the way area, though I have found you'll almost never need to waste the time doing this outside of maybe one or two songs.

I will spam songs if say I need a certain % for an edge, but otherwise I find most of them go up pretty reliably just through ordinary use.

>Is it true that only invokers can learn spells on low level
>mobs?

Invokers don't work differently than anyone else for learning, with the exception of affinity (which isn't relevant to this).

>I've spammed things like fireball and such on low level mobs,
>to practice them, because if I only cast while leveling, I'd
>get to 38 still on the second tier of spells....

That's true if you're a 7 path invoker.

>My question is...for classes like bards, necros, druids,
>shamans...that have cast/commune/song options that are really
>important to competing in pk, are they incapable of learning
>while not ranking by casting on loads of lower level mobs like
>invokers can?

It's always hard to learn an offensive spell by casting it on something way-ass lower level than you are. Really, really hard. Even if you're an invoker.