I totally get your concern about the drifting issue with your Michelin Alpin 6 winter tires. It's frustrating when you invest in new tires, expecting an improvement, and then experience an unexpected problem. I haven't personally used that specific tire model on my IS300h, but it's interesting to hear about your situation.
It's good that you've taken the initiative to check with the tire shop and even consulted the Lexus dealer. It's a bit alarming that they suggested the drifting might be related to the tire tread, specifically the V-shaped pattern. I can see how having a directional design could potentially lead to such issues.