Well, if all your fellow passengers trust the checked bag system, you can be assured of cabin bag space.

But they don't, so you can't.

P.S.

1. I saw the discussion in Delta Basic vs Main Seats Overhead Bins Question? , and what moondog said. You aren’t going to get different answers here, as much as you want the answer to be different.

2. AA EXP FB group does have people who board late and have to carry in hand their electronics onboard. Or they don’t fly.