But OP has a point (to a point). I have been a "BMW person" for about 14 years. BMW offers nicer, more luxurious features in the 5 series vs the 3 (for example). Nicer leather options, more customization, more color options (or more ability to participate in their "individual" program to order off menu colors etc for additional costs).
These are in addition to the engine options etc. I was a BMW 3/4 series driver, my wife is an X5 driver. I bought the Tesla Model 3 P instead of another BMW, as I didnt want the larger 5 series. The pricing was similar.. I could have gotten a BMW 540 nicely equipped for what I paid for the model 3 performance. The 5 series is a completely different level of luxury comparatively to any 3/4
The interior of a model S is not appreciably nicer than a model 3 at this particular point, at least in my opinion. its just bigger, and the cost of the vehicle new does not match the level of "luxury" you get from those other brands. There is more to a vehicle than luxury, of course, but there should be some more differentiation in the interior for model S (and X) vehicles.