My opinion? The hardest hill you do will never be effortless.

"Effortless" hills are the ones that are so low on your scale of what's a hill, that you don't notice them any more. People who seem to take your hill so easily probably train on much steeper and/or longer ones.

That would be my thinking, anyway. I occasionally ride with people who are much stronger than I am, pretty much the strongest riders in my area, and the toughest hills we do are still an effort for them. A lot easier for them than they are for me - but still an effort.

From the opposite perspective, there's a hill on TOSRV that, to us hillbillies, literally is not a hill, but to the many Columbusites who ride that ride, is quite daunting.