Do Jedi not use their powers "efficiently," or do we as fans not have a clearly defined explanation on how their powers work and what the use of them requires?
We have an explanation. It is an energy field created by all living things and so on and so forth (I don't remember the exact quote), which implies a huge amount of energy that "force users" are tapping into, given the number of living things in the Star Wars universe. Additionally, Yoda lifted a space ship and said that the size didn't matter. On top of that, we have plenty of examples of how the force is used, such as the "force push" introduced in the PT, and the light saber retrieval. Both of those things are done routinely with no evidence of physical effort or strain in most cases.
We can think that the Force is an unlimited and effortless superpower despite the fact that at NO POINT IN THE MOVIES does it appear to be this.
Most of the stuff they do with the force appears to be effortless. Yoda tells Luke that it is unlimited, and then proceeds to lift a space ship; and he wasn't exactly grunting and straining while doing so either.
If it is indeed unlimited and effortless as you suggest, (apparently based entirely on one line),
The movie suggests this, through dialog and examples. In fact, for the dialog, it wasn't simply suggested, it was flat-out stated.
then we have to assume all the Jedi are complete morons.
Yes, and it is the fault of the writer(s) of course.
This option has the advantage of making us feel both smarter than Lucas ("I wouldn't have written it that badly.") and smarter than Jedi ("I'd use the force better than stupid Yoda.")
Say what? Who cares if they are smarter than George Lucas (much less his fictional characters)? He's obviously above average in intelligence, but then, so is half the world's population. He's not exactly Einstein or Archimedes however.
Or we can assume these Jedi Masters actually know how to use the Force but that there are some practical limits to the Force, both in quanitifiable means (how heavy an object you can move) and practical means (why not make your lightsaber instantly fly back to you, why not use the force when flying a starfighter), even if the exact and specific limits are unclear.
So your argument is that the force and the use thereof is essentially random and neither examples of its use/nature nor direct statements regarding its use/nature can be trusted? If that's the case, then that's dodgy writing too.
BTW, the "exact and specific limits" are not unclear; at least not with regard to the size of an object that can be moved with telekinesis. The size doesn't matter, as stated by Yoda in ESB. I know you think Yoda was just making stuff up, but there is no evidence of this. Making a claim along the lines of: "Well if Yoda really meant what he clearly said, then that would mean the Jedi were morons," is not evidence that Yoda didn't mean what he said; it is simply "begging the question" on your part.