I have heard just a few naysayers with no evidence regarding the use of universal grade oil in non diesel engines. I have heard two reasons of which I am skeptical. Your reason is the third and I can't understand your mechanics response at all. The only difference in Universal grade and others is increased amounts of soot dispersal and other cleaning additives. The viscosity is the same as any other oil of the same viscosity, thus having no effect on oil pressure.
Just so you'll know the other two reasons which I believe are unsubstantiated, they are; "U grade will foul spark plugs", and "U grade will hurt catalytic converters". If these were true, how would this grade earn S(spark ignited) as well as C(compression ignited) ratings. I have run Delo in everything from lawn mower to 300E with great success. My 300E has about 179,000 on it now with no oil related problems, the same catalytic converter, and I have run the same spark plugs so long that I'm ashamed of myself.