when returning car and having lots of luggage; does it make sense to drop off luggage at terminal before returning car?

First dropping of the luggage than bringing back the car, I would say no, because you can go buy bus or little train to the gate at the airport. Thank you for asking

Use sky cap

You can't leave the car at the curb to check the luggage, so if you are alone you have to take it on the sky train with you OR use curbside check in but you should check with your airline how that works. BTW I'm an older woman travelling alone and I managed sky train, but you need to use elevators, not escalators.

Only if you have someone to stay with the luggage.

Yes.