>> And what is "regular" maintenance on a grease fitting-free sealed and not serviceable component?
I can't tell if you are asking that seriously or not. But, assuming you honestly don't know, "regular maintenance" on ball joints is to replace them when they wear out, which is evidenced by improper motion of the joint when the suspension is unloaded.
There are many wear-out-and-replace parts on a car, even one without an internal combustion engine. Shocks, struts, strut spring seats, strut steering bearings, control arm bushings, ball joints, steering bushings, sway bar and sway bar end link bushings, motor mount bushings (I honestly don't know if Tesla's electric motors ride on bushing mounts, though), and in recent times, brake rotors and even whole transmissions (Ford 6F35 and Aisin Warner AW55 as examples) have made it onto the "wear out and replace" list of maintenance items.
A long time ago, most joints on a vehicle were not sealed and had grease fittings so that the joints could be cleaned out and relubricated. These types of joints lasted forever with regular maintenance. Everything started to go sealed/maintenance free when people got tired of constantly having to have this maintenance done, and demanded cars you could drive 50,000 miles without having to lay a wrench on except for oil changes. That figure today is more like 150,000 miles, and some car companies even warrant their drivetrains for 100k miles or 10 years.
$3,100 is actually insane for a control arm and ball joint. $310 would still be insane for a single side. I think I paid about $300 for a set of both front LCAs and ball joints on my Volvo, and that's a Volvo so it's already expensive compared to, say, a Chevy Cobalt.
None of this or your response is relevant to the fact that all parties involved are being dicks to each other about it, and to the fact that the Mom's Basement Commando crowd is all too willing to go to war over it.