This must be an optimization issue or something. OW2 is the exactly the same as OW1, nothing has changed in regards to sensitivity (or the base game in general). I can tell you with 100% certainty that the base sensitivity is the same, no question about it.
But multiple reports of it feeling different must mean there is something going on.
Whether it's related to smoothing, FPS, polling rate, vsync, gpu, cpu or whatever else I don't know.
If someone has the issue and finds a solution, let us know!