No, the carry-on is a piece of luggage that can be stored in the overhead compartment (assuming there’s room, hence the waiting in line). In addition you can bring a personal item (backpack/purse). It’s those bags being put up top as well where the dick moves come in since, on a full flight, there’s not enough space up there and the passengers who boarded before you have put BOTH their carry-on and personal item up there.

With the backpack I have, I do lose a good part of my leg space from having my backpack underneath the seat in front of me. That's why I sometimes pull my backpack out and then set it down in front of me, but not underneath the seat in front of me; this lets me stretch/move my legs more than before.

Wish I had your luck. I've had issues three times with checked bags in the last 15 years.

Lucky. I stopped checking bags when the baggage handlers stole from my locked suitcase.