I've had 700 kg cars that rivalled sports cars for grip and ability to accelerate. To say that sub 1 ton cars are going to be unpleasant to drive at highway speeds is a statement that does not jive with my 43 years of driving experience on three continents and in many types of vehicle and road conditions.
What is far more important than total mass is mass distribution, width of the tires (which can be an advantage and a disadvantage depending on the conditions) and traction model. Noise is a function of isolation and shape of the body and road contact and here lighter cars have the advantage: substantially reduced tire noise.
I don't think it's impossible to have a small car that drives great - I drove a CR-X as a starter car and upgraded to a 00's Celica. I think the likelihood of a sub-1-tonne EV being specced outside of it's intended market niche at this price point in this stage of corporate wealth hoarding is extremely low. If it does turn up that the car is well-suited for highway driving, I'm happy to eat crow but that doesn't mean that I won't still think the probability of the inverse is higher until that point.