Bilstein make very decent dampers, it's just that for whatever reason in some applications they don't quite get it right, but a mass-produced OEM damper is often just trying to be all things to all people. Also, the customer in one country may have different expectations to a customer in another, so a 'one size fits all' approach is going to cause some issues.
BMW suspension when they were only selling cars with runflats, was really awful on UK roads. Probably OK on the Autobahn with 4 people and a trunk full of luggage ferrying people to and from the airport, but terrible for a bit of spirited driving on your own around country lanes.
My last ICE car started off as a 3 series with runflats and that horrible factory suspension. I put proper tyres on it and got a set of Bilsteins fitted and the car was transformed. Now it's very likely the factory dampers on my car were Bilsteins, but the ones I swapped them for were very different as the damping curves and spring rates had been customised for my particular model and for use with non-runflats on UK roads.
So regardless of who makes Model Y dampers for Tesla, it's not all their fault you're not getting on with them. They are no doubt being made to a very low price point and with valving and springs which are supposed to work anywhere in the world, with any load, on any roads and with several different wheel/tyre configurations. This is why more and more Tesla owners seem to be turning to aftermarket coilovers for their cars and that is the only solution IMO.