So I've never had a car with mirror blind spot warnings (or any blind spot warnings) so I can't talk about missing them. That said, I can say the on screen view of the cars around you does not help me when changing lanes.. Cars fall off the screen before they are far enough away for me to want to move into the lane... .so I still do the look over the shoulder thing and I will tell you I feel like the passenger side blind spot is harder to see vs my old Camry.
Now there is talk that Tesla will add the view from the side camera in the main screen when the blinker turns on... now that I think would be fantastic and that I would use because it will be way better than what I could see- but I hope its the entire main part of the screen, not just a small window like when you back up because I want to see it all in a quick glance at the screen.
I will add that when you are in autopilot, its less of a concern because of 2 things- 1) autopilot detects that its safe to move into a lane because it shows the lane in blue (I still use the confirm setting in lane changing) and 2) when in autopilot I can actually take longer to look at the blind spot because the car is doing most of the driving.
That's my 2 cents.