I think the most important thing to tell beginners is that in the end music is whatever anyone makes of it. Otherwise how do you explain people liking Stockhausen and at the same time Jimi Hendrix? There's all sorts of things and there really are no "rules" at all. There's of course the physical and cognitive aspects of music and how it's perceived by the brain, but there's a rather big margin for subjectiveness added to this.
You can really just as well not learn any theory and just go by ear, there's absolutely nothing wrong with that. But I'm of course in favor of researching (not theory in specific, but just looking up literature/other composers/styles, etc) but you don't really HAVE to.
Plus you're missing the 20th century "classical" music stuff like Ligeti/Cage/Boulez/Reich and so on. Modernism in general and even guys like Debussy are super important (specially to things like bossa and a lot of jazz.)
PS: Oh to guys saying "hur hur theory is a recent thing!" Yeah sure it is, Rameau in 1722 sure thought it was rather up to date when he released his Treatise on Harmony. Nevermind of course the whole ars nova deal centuries earlier! Come on theory has been around literally as long as music has, but it has always taken different shapes depending on the time it was practiced (and the literature they had access to.) You can even argue that chord anatomy was already studied as such so long as there was a shift to vertical at the beginning of the baroque period (post-palestrina.)