I think that the cross-class abilities are meant to fit that bill, and effectively give you as much control over your character as the current WoW talent system.. with the proviso that you have to put the hours in to get those classes leveled.
Except I HAVE to be missing something, cause I see maybe one good cross skill ability white mages can get access to, which is terrible. If I'm reading a chart correctly, they can only pair off with THM and ACN, and of those THM gives Thunder 2(don't care), Surecase(shouldn't be getting hit to make you care), and Swiftcast(is awesome), while ACN gives you Ruin(don't care), Bio(don't care), Virus(slightly can lower tank damage I guess), and Eye for an Eye(lowers tank damage by 10% maybe at times on a low chance random proc, a bane of any healer).
So yeah, as a healer, I get absolutely nothing from this system, go me? And after leveling a class leveling *another* class to +30 is not the same as leveling a class and spec'ing into something. Personally, I think not having a tree is one of the game's biggest mistakes given how bad the cross class system works. /shrug