As for the 4 ton for 2100 square feet, it's my understanding that 1 ton
is suggested per 500 square feet, so 4 tons for 2000 square feet. Is
this not correct?

This is a perfect example of a really, really bad way to size an A/C. Your
contractor should have done Manual J and Manual D calculations which take into
account things like insulation, windows, building orientation and duct size.