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I have been playing Runescape for 10 years, the entire time F2P AND PROUD. I've made every conceivable type of character and a few of my own experimental builds. Having said that, Runescape magic is limited by a major factor, cost. Leveling magic is ridiculously easy, you can get it to 59 in a couple days, levels don't matter. If you have money to throw around in that game, you have it made in every gameplay aspect, regardless of player skill.
Frankly put, magic is fueled by money. But the problem isn't money.
The problem is rooted in basic supply and demand, caused by Jagex's own GREED.
The only runes a f2p character can craft are the elemental runes which can just be substituted by elemental staves. Elemental runes are insanely cheap and easy to get on the GE. Combat runes, needed by every single mage spell, can only be crafted by Members. There are way more F2P players than members, plus somebody paying monthly isn't going to waste much time runecrafting (or bot), they would rather see all the cool member's stuff than the same 3 places over and over.
In short. Combat runes are in too low of a supply to support the player population, this has always been the case and it is why there is a shortage of mages (and coincidentally rangers) and a huge surplus of melee pures. This has been the natural order of things for the last 10 years with no attention from Jagex.
Unless you can afford it, or afford to support it, or unless you don't feel like supporting that expensive habit, you cannot practice magic in Runescape. Period.
p.s. Rangers have it easy, at least for pve.