Of course it's easier to pull back the slide with the hammer out of the way. The question is whether it would be worthwhile to do so, and whether it's something you would want to attempt in a stressful situation. Hence, it's dependent on the gun, your physical condition, the shape of the hammer, etc.

To be brutally honest--if the slide is that difficult for a shooter to operate (even one-handed), then I do not think that it's a very good choice. Most "decent" guns I see don't come close to being all that hard at all to manipulate. It's Tauruses, for the most part.

Oh, and I'd suggest exercising caution when attempting this with a 1911. The reason being that slipping and allowing the hammer to fall would result in the half-cock notch slamming into the sear, which is not super-great for the engagement surface (sear nose). The half-cock notch is a once-in-a-long-while-or-maybe-never safety feature, not something you want to ever want to use intentionally.

Last Edit, I swear: True story, I see idiots manually lowering the hammer on their 1911s all the time. Several times a month, a class blows in to qualify, and there's always two or three guys with 1911s. Sometimes even expensive brands (if not good ones, but that's another thread). And without fail, one of them decides to de-cock the gun for holstering by lowering it with his thumb without keeping the trigger depressed. For reasons known only to him.

So if one is determined to manually lower the hammer (pro-tip: dry-firing on the "hammer down" command ensures the chamber is empty, which is what we want), keep the trigger pinned against the frame until the hammer is all the way down. Otherwise you're just grinding the half-cock notch against the sear nose.