LOTR has lots of downtime? Sure, there's like fifty or sixty years at the beginning, but, after Frodo leaves the Shire, what significant downtime is there? A couple of weeks with the elves and again with the elves, but, other than that, not a whole lot. By the Return of the King, there's almost no downtime as I recall. From the breaking of the Fellowship to the fall of Mordor, there's what, a single year? In that time, Pippin and Merry go from being very low level fighters to pretty high level ones.
Never mind that the Hobbit takes about a year as well.
The Belgariad, from the time Garion leaves his home to becoming King is about two years. Helpless peon to world-shattering God-mage in a couple of years. Not too shabby.
I think JM has a good point here. Most heroic fantasy works don't include major downtime. Heck, Conan goes from being a wandering homeless guy to king in a matter of a couple of years, depending on how you count.