Your analogy is correct about the shorting- but it takes effort (work) to move the iron armature (or pole pieces) through the magnetic force. Regardless of the structure (magnet flux). It may be easier to move through 360 degrees with a well designed armature/field but it would take the same effort to produce the same power (electrical energy) if it is produced in 90 degrees or 360 . . . (or with the bad design you could use a flywheel, or some other mechanical means to smooth the effort required)
I have a 120 vdc generator (from the 40's) and if I add any kind of real field voltage (excitation) on it, it seems to lock up (as far as one's hands trying to turn it are concerned)
No such thing as a free lunch. You want to generate electricity . . it takes work.
Now, how much and how does it compare to the "grid' - a few years back I did the arithmetic, buying an alternator, buying fuel, buying the ancillary items (shed for the alternator, regular maintenance (air and fuel filters), radiator flushes, depreciation, lubricating oil, etc. etc).. I could just generate energy at the point where the power company is selling it to me . . .
Now my opinion . . . the utility company probably tracks this stuff more closely than I do . . it will always be just a little tiny bit cheaper to buy power than make it (hydro, wind, solar cells, geothermal, tides, notwithstanding).
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