Yes they are comparing SYSTEMS. If one is designed to use DIMMs and the other LPDDR then that's how you should compare them. If you were comparing a PC laptop with a Mac laptop would you say "it is unfair comparing performance because Apple uses LPDDR" but think it is fine comparing expandability? I agree it is not a valid comparison of x86 and ARM but it is a valid comparison between two systems, which were made differently as their respective OEMs made different decisions along the way.
And N5 vs N4 is pretty minor. If it was N7/N6 vs N5/N4 that might be more valid but if both systems were shipping at the time of the comparison then how would be it be the fault of the one using N4 that the other was using N6? The tradeoff for that decision leading to worse performance would be lower cost to make the chips, same as the tradeoff between higher memory bandwidth vs ability to expand memory in DIMMs vs LPDDR.