Skill trees are nice in games designed around it, XI/XIV for example are more designed around that jobs are predefined roles (FF game after all), so while there's people who want to be a WHM with a pure focus on nuking and melee and saying fuck curing, that's not gonna happen most likely xD

Side note, the only reason prices shot up on materia (certain ones) is due to Relics, otherwise there's more than enough supply to meet demand which drops prices, not raises them.