'I believe they checked all bushings and links (all of which had been replaced, anyway), they checked to see if steering was too tight, tire pressure, and noticed a small amount of feathering particularly on my front left tire.'
'My front left tire typically shows a bit more feathering than any other tire, and the rears look like they're wearing perfect.'
Quick diagnostic: swap wheels front and rear and see if things improve. If so, the alignment is NOT right, and/or parts are worn you haven't located. When I did this, dramatic change in handling, even though all tires looked pretty good. I left the tires this way when getting the alignment.
Note too if you are just visually checking the rear suspension, you won't see loose mounting bolts. Everything looked fine on our 190E, but vigorously shaking the rear wheels while on the ground showed SOMETHING loose on one side. Turned out to be a track strut bolt.
Test the steering with wheels on the ground. Watch for what moves while someone turns the steering wheel just until resistance is felt (engine off). You'll see what moves the wrong way at the pivots. I found too much play in the idler bushings - easy replacement.