Superchargers put more strain on the engine because to make the same WHP the engine has to put out a much higher output before the massive parasitic loss of driving the supercharger is factored in. A centrifugal blower may put less strain on an engine than a turbo kit by virtue of running low boost through peak torque range and ramping up boost as revs rise, keeping torque closer to a straight line, but you can do the same thing with a turbo kit and a good boost controller. It's the difference between 2 pounds at 3500 rpm and 10 pounds at 6000 and the full 10 pounds from 3500 to 6000 that makes a turbocharger "harder" on an engine, if anything. That also means more power in the form of torque through the rev range, though.