*shrugs*
Whilst it has been RM's "official" POV since the beginning, I've been for decades in disagreement with how the rules do not have a care about the matter, and classify spells (and professions) according to said realms. I wrote (complained?) about the matter many times but the rules don't see realms as the source (the "how") of magic but the effects (the "what") themselves, as what realm one uses dictates what one can do (and which kind of spells one may cast) rather than how one fuels one's spells. It's similar to electricity: the realms are the "sources", may it be nuclear, hydro, wind, charcoal, but once one gets electricity, one may perform the same actions, regardless of the original source.
As far as I'm concerned, whilst I do it differently from Peter Mork, I changed the RM magic system so as to focus more on the realms as sources than on the resulting effects. For one thing, I don't separate spell lists or professions as being part of one realm: in my system, there are only Open, Closed and Base lists, and they are completely independent of the notion of "realm".
I then have rules focusing on the differences of being a user of Essence Magic, Personal Magic ("Mentalism") or Divine Magic ("Channeling"), but each of them may acquire any Open or Closed spell list exactly the same. Similarly, for instance, a Magician may equally be a user of Essence Magic, Personal Magic or Divine Magic, with no difference in how hard (or easy) he acquires his spell lists, the difference laying on his own nature as a Essence, Personal or Divine spellcaster.