I believe the video is valid. Unless you were driving on an un-paved road or a concrete surface that has lines etched in them. The amount of driver steering input that is see, is not normal. This a finely tuned machine and all 10 of my Audi’s have never ever done this. From driving the cross Bronx in NYC to the 80 mph roads of Montana. If balance, alignment and suspension components check out, then it is the tires. All of these checks should have been covered by the dealership/Audi. Your service consultant should have grabbed a tech and all 3 of you go for a ride to show wandering. That’s what my dealership did and always does ( maybe why my service writer places top 3 in the country every year for service consultants and the tech places same). You are more than welcome to PM me for tips on how to handle your situation.

thanks for your input, very valuable to me. (see my post about road staightness).

i am back and forth on tires vs steering issues. it's eye-opening to me that there ARE pirelli 21's out there (these are all non-RF's as pirelli doesn't make a RF in that size) that do Not wander. which suggests steering issues.
otoh, we also have at least one person who has pirelli's with exactly the same issue.

as for driving it w the service tech (in my case the mngr), i have driven both a new q7 w Pirelli's (21) and mine, back to back, but the road and speed (limited to 50 or so) needed weren't available. and while i could tell a difference even at 50, he couldn't. thus the video's at 74mph.

the other guy w the issue has shared his contact info and he is very near me in Miami, and adjacent dealer amazingly, and they will compare notes, as i bring it in again on monday.

i am hoping for everyone's sake that it proves not to be the tires, as 21" options are limited, and i see some struggling with choices.

i'll report back.