It's valid to say that Tesla aren't up with the German players for interior quality, but it's a bit unrealistic expecting them to be, given they've only been making cars in larger volumes for about 8 years. It's an extremely difficult undertaking, and the learning curve is steep.
The established brands don't always get it right though. Most of us know about the poor interior of the E60, particularly pre-facelift. The W204 C-Class was well below par inside too. Several Mercedes models were a let down inside given the reputation of the brand and cost. The F30 is nothing to write home about in terms of interior quality either. Audi has been the best performer on this metric, their cabins always seem to have the perceived (or actual) finish expected- they didn't even cut corners on the A2, A1 and A3 , given their price and category.
The Model 3 looks better than the S, and there's every chance subsequent generations will be better still. Hyundai and Kia are another example- it probably took them what, 20 years to achieve parity with the big mainstream players? And that was just to rival Ford, Peugeot and VW, etc.