I agree that it's "incredible", but only if you use like it was built to be used: on a full frame camera.
Using it on an R7 with a 1.6x crop factor reduces that 28-70mm f/2 to an equivalent 45-112mm f3.2.
Tamron has an excellent 35-135mm f2-2.8 for full frame. That's 1.4 stops faster than the...