This will sound odd, but...what software version did your car have when you picked it up?
Did you get a software update at any point around this saga?
About a year ago a bunch of us on these forums noticed increased power assist / reduced steering effort on our Model 3's after a software update. And reduce difference between steering modes. The change was most apparent at lower speeds though, where the steering became (and still is) overboosted to the point where it feels *lighter* at low speeds than at high speeds - which is the exact opposite of how steering naturally feels (in the absence of power assist).
https://teslamotorsclub.com/tmc/threads/sports-mode-steering-feels-significantly-lighter.265076/
I complained to my local service center when it happened but of course they couldn't do anything about it. Tesla has never fixed that. To this day, my 2021 M3P still has the new overboosted steering. A 2020 M3LR loaner I had recently, which was running recent software too of course, was no better. (Actually it was worse because its suspension and tires were worse than mine, but that was expected.)
After a while the acute memory of my car's previous power assist programming began fading, and eventually I began questioning if the car really ever had the better power assist that I remembered. Then recently I took a 2023 (or maybe late 2022) MYLR for a very brief, very low speed spin only inside a parking garage - and it still had the old, better power assist programming. The difference was obvious. To be clear, my Model 3 has vastly better steering
response than that Model Y - but the Y still had the better power assist programming from before Tesla messed it up on the Model 3. (Now that MYLR also had much heavier wheels than those on my Model 3, and wheel weight directly affects steering effort, but I'm pretty confident the difference was from much more than just the heavier wheels.)
And then I test drove a Palladium Model S (the current Model S). It too had power assist programming reminiscent of what my Model 3 used to have. So I'm back to feeling very confident that Tesla really did mess up the Model 3's power steering programming.
Like any electronic device with software, when Tesla manufactures a car, they will use a software revision or branch that has been thoroughly tested for use as the software that ships from the factory. That software version will often be much older than what is currently being served in automatic updates. It is plausible to me that your Model 3, as new as it is, came with the old power assist programming. And now you have the newer, worse power assist programming.
Edit: All that said, the change for worse power steering was (is) most apparent at low speeds, not so much at high speeds. And it did NOT make the car feel unstable. It was just a power steering change, no change to actual suspension behavior of course. (There is no software control over the suspension in this car.)