You are still asking the system to do a lot in 700 pages if you expect balanced and expansive options. A Tolkien elf is not an Eberron elf. Aragorn and Drizzt are not the same type of rangers. Magic is wildly different in Middle Earth, Hyboria, Greyhawk and Hogwarts (to the point where you can't have one universal wizard class that could emulate them all, low/high module be damned). Their is no One System to Play Them All. Nor would I necessarily want that: a system so disassociated from it's source material doesn't have anything to focus it. It would be easily abused when modules designed for one type of play mix with a different (Harry Potter magic meets Westros healing/combat).
The d20 system showed it was remarkably flexible. It did that by creating hundreds of separate games with their own tweaks and versions of things. It constantly reinvented the wheel. And despite being similar enough, they weren't compatible without a lot of elbow grease (speaking from experience as someone who ran a SWRE Jedi in a "D&D" campaign). No way could you do the same in just 700 pages.