The Tesla is not a supercar. It's a luxury car. Its competitors are BMW/Mercedes-type luxury cars. Just because a car is $150k does not make it a supercar.
The average family sedan does 180km/h on there — so a Tesla at 160km/h will seem slow.
Get a Tesla on a race track with any decent mid-range car for a 200 mile race and see what happens.
But a Tesla is a supercar in terms of performance. No other BMW/Mercedes/Audi in the price range will touch its acceleration. It rivals a Lamborghini Aventador.
But overall you're right. Supercar isn't really the right word for Tesla.
Maybe Teslas aren't supercars, but they're instead super cars?