The takeoff has already happened, and a landing (of some sort) will have to happen (which also means flying near ground level).

The thing that doesn't need to happen is flying at full flight altitude when the pressure differential between the inside and outside is greatest.

Incorrect. In level flight the wings have - by definition - 1g of upward load. Regardless of speed or altitude.

That’s what sand worm was saying - level flight puts less stress on the wings than takeoff (where you accelerate vertically, thus have more than 1g).

Still, you don’t want to take a structurally damaged plane high up.

Consider cabin pressure differential versus the outside ambient air.

1g in up/down force. But thicker air means more forwards/back forces. Higher engine power = more force, regardless of G.

Engine power is a fraction of weight. Even at full thrust (which is rarely used in commercial service, even for takeoff), the engines are only capable of 0.25g or so.