There are people who think they are productive and working fast and then there are those who really are. My wife thinks she is getting the groceries up in a hurry but meanwhile I've made 2 trips out to the car and back. Same goes with LCO's and lawns. People just work at different paces. One man's fast is another's glacial. One guy is knocking them out on a ZTR while another thinks he's flying through lawns with his 36" gear drive machine.
I can tell a distinct difference in some situations between a 460 model and a 755 model backpack blower in how fast a job gets done. If you can't see how a backpack would be faster then you're probably not into the whole speed thing or you have unusually light clippings and debris to handle. They move more air and move it faster. It's not that complicated. Can you jog with a handheld and still keep the debris ahead of you? If not it's slower.
As for starting up an experienced user hits choke, one pull, then dechokes it and and cranks it and in one motion is slinging on and blowing. What are you saving, 1.5 seconds? You could make an argument for the added weight of a backpack blower that one has to lift over a trailer rail, but then that's way offset by having to lug a blower around in a single hand.
And seeing as one can blow about 5,000 residential lawns with a backpack blower before it even starts wearing out, I'm thinking the $150-$250 price differential is pretty insignificant.