Nor are you taking into account the fact that the only substantial wimax provider in the United States at the time (and maybe even the world? I don't know) was broadcasting at 2.5 ghz. Signals at that frequency do not propagate very well (distance wise) nor through many structures. That was, of course, related to Clear's spectrum holdings at the time.
But, yeah, as people migrated off wimax to LTE devices, more bandwidth was freed up, allowing for faster DL speeds. Several of us here in Atlanta noticed that as well.
Once all 3 bands are fully deployed with "Spark," I'm sure you'll be even more impressed.