I have some people at work who
really want a Tesla. Like they would never ever consider spending 100k Euro on a Merc S class or an Audi A8, but they are willing to take on a huge financial commitment just to drive a Tesla - it's a brand + hype thing. I suspect that most of them will end up getting a Model 3 instead since that's far more into their price bracket.
I still think you are right - if you can "easily" drop 100k on a model S you are not going to buy the Model 3 instead. But if you were saving up for a model S and would have eventually bought it had Model 3 not became available, then yeah, Model 3 has just cannibalized those sales.