I think this is the crux of it. Different brands prioritize different things and the consumers that are loyal to those brands tend to value the things that brand prioritizes. I don't care about plush interiors much, they are actually a source of stress for me because I am always concerned about messing them up. I just want a really fast car with a solid stereo that looks good, can fit my family and sports gear, and is cheap to operate. The model 3 checks all of those boxes better than any car I have seen... supercar level performance, integrated spotify with decent speakers and a subwoofer, 4 door sedan with ample storage, and I spent $275 last year in electricity to drive the car. Sure, if I had my druthers the P3D would get more aggressive styling and a sportier suspension from the factory, but overall I really can't complain too much. My P3D is the best car I have ever owned and it isn't even close.I think the disconnect is that you seem to expect the Tesla to be everything a Tesla is - PLUS everything a Mercedes is - at the price of a Mercedes.
There's no Honda or Mecedes with Tesla-level integrated infotainment or app-control. And there's no Honda or Mercedes with Tesla-level performance or drivability. Yet the Tesla has a lower total cost of ownership than either. If those things appeal to you, Tesla may be a good choice. But if your priorities are fancy seat stitching and Android Auto, you're going to hate Tesla. There's nothing wrong with that, but there's no need for you to keep whining about Tesla not having fancier interiors. Go get an i5 and enjoy everything that Tesla is not.
As far as the Highland speculation goes. My hopes would be 0-60 in 2.8 or less, adjustable ride height suspension, and some kind of body kit or unique fenders to set it apart from the other trims. It really doesn't matter what I think though because my wife will never let me get a new car in the next 5 years.