So, if I'm just totally outnumbered on the idea of other classes having unique spells, why not just...remove spellcasting from all but the sorcerer?
Seriously, I just don't see the point of them being spellcasters if it isn't possible that any ranger in history has ever developed a spell that requires training as a ranger. Might as well give them magical thematical abilities that entirely bypass spell slots and the spellcasting feature, and if you want them tied to druids, give them druidic ritual casting.