70 cropped to 105 is not bad, 105 cropped to 150 is not bad. 70 cropped to 150 is not good.
A broader lens zoom range that doesn't sacrifice IQ is a good thing. Trading a stop of light is ok in a walk around lens, for me at least, although having something fast for low light indoors is often useful.
I view the 28-70/2 a less of a zoom lens and more of a collection of fast primes.