Two thoughts occur to me.

First, we can model an ideal gas by allowing that there are short-range repulsive forces between molecules (the 'hard spheres' model), and the molecules are of negligible size. In this model we will find that both Boyle's law holds and the internal energy is a function of temperature alone, so such a gas is correctly called ideal. In this case the standard argument about pressure gradient from forces on a thin parcel of gas will hold since each parcel of gas does indeed exert a force on surrounding parcels.

If, on the other hand, you want to think of the gas particles as never even hitting each other, then the thermalization takes places via collisions with the walls. In this case I think the standard treatment of chemical potential still holds and you can use an entropy argument to show that the density (and hence the pressure) is uniform in the absence of gravity, and there is a density gradient (and hence a pressure gradient) in the presence of gravity.

Two thoughts occur to me.

First, we can model an ideal gas by allowing that there are short-range repulsive forces between molecules (the 'hard spheres' model), and the molecules themselves take up a negligible volume compared to that of the chamber holding the gas. In this model we will find that both Boyle's law holds and the internal energy is a function of temperature alone, so such a gas is correctly called ideal. In this case the standard argument about pressure gradient from forces on a thin parcel of gas will hold since each parcel of gas does indeed exert a force on surrounding parcels.

If, on the other hand, you want to think of the gas particles as never even hitting each other, then the thermalization takes place via collisions with the walls. In this case I think the standard treatment of chemical potential still holds and you can use an entropy argument to show that the density (and hence the pressure) is uniform in the absence of gravity, and there is a density gradient (and hence a pressure gradient) in the presence of gravity.

(I note that in the question you say an ideal gas is not ergodic and would never reach equilibrium. In order to maintain that you would have to treat collisions with walls as either not happening at all or else acting like simple reflections, which is not the case. I have pointed out above that in order for a gas to be ideal is not necessary for inter-particle collisions to be negligible. But even if you insist on reserving the term 'ideal' for a model with no inter-particle collisions at all (which I think would be a non-standard terminology), then collisions with the walls would still suffice to produce ergodic behaviour.)