I must agree that some people have a harder time with high cadence than others. That is particularly true with heavier legs. However 70 does seem too low. It's not just efficiency, either. The higher cadence is better at encouraging aerobic exertion and increased blood supply to the muscles. You have to have a good fuel delivery system for an engine to run well, and in the case of muscles, to increase horsepower.
It is sadly not unusual for a "tune-up to be done with no wheel removal, which means if you have not checked them t hat the wheel bearings could be running tight. Don't just check for play - they need to be removed. You should be able to turn the axle with very little resistance, no catching, and if q/r there should be a little up/down play when not mounted. If they are tight return to the shop and ask the head mechanic to go back over the entire bike. Anyone who would skip hubs probably left other items improperly done as well.