Under ideal operating conditions starting motors operate under virtually "dead short" resistance. That's why they're only intended to be run for a few seconds at a time. If an engine is cranked for 30 seconds without starting the starter needs 20 minutes of cool-down time before another attempt at starting is made. A well-tuned engine probably won't run the starter for even 5 seconds before the engine fires. As long as the starter is running at its normal speed, a magnetic induction known as "counter-EMF" controls the maximum current draw to some extent. If the engine is hard to crank due to sticky piston rings, cold oil, etc. the starter can't achieve its normal cranking speed and the current draw increases dramatically. Just a few seconds of cranking very slowly under heavy load can destroy the windings in the starter due to excessive current draw.

It sounds like you have destroyed the starter internally from excessive current draw. Now the only option will be to dismantle everything and see if there's anything left to repair. if the engine can't be turned easily by pushing the vehicle in high gear with the spark plugs removed, find out why it's hard to turn before you try to spin it over it with the starter again.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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