Yeah, the ? is to highlight that I'm unsure. It's my take on it, but as we're on the internets and opinions always comes across with the elbow first I think a ? makes it a bit... gentler :)
As the Prius is a hybrid, can you really compare them straight up?
The Prius might very well have had more positive impact on the environment than the Tesla, but when it comes to pushing tech, like you say, and peoples positive perception of electric vehicles I think the Tesla has done more.
I highly doubt VW, BMW, Volvo, etc would've been so keen electric cars as they are today if it wasn't for Tesla.