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You discredit yourself by using such a totaly ridiculous exampls as a 7.5 HP three phase shop motor compared with a specifically designed garden tractor engine. Why don't yo try putting that tractor engine to use in place of the shop motor if you think it is so much better?

You could very well use that tractor engine in place of the electric motor on a hp for hp basis. The main reasons to use the heavy electric motor are that you don't have a lot of fumes, it's quieter, and you don't have to keep a supply of fuel on hand.

One application for such motors is air compressors. Depending on use, some use IC engines, some use electric motors.

You could very well use that tractor engine in place of the electric motor on a hp for hp basis.

No. You couldn't. HP ratings, and torque curves, are very different for electric motors and gasoline engines. They are rated so differently that comparing the ratings number for number is as meaningless as comparing grams and ounces without knowing that they are different units of measure.

Here is some information on this difference for your reference.