It's funny how you don't think there would be that much of a difference between the GP-100, and the L frame as compared to the K frame. But when you put them on you do feel it. The S&W 19 you tried had a 4" barrel which means it should have had a square butt. The round butt and shorter barrel will make it feel much more compact but they are made of steel and you can't get away from the weight. You may also appreciate the weight when shooting .357 loads as if helps with recoil and follow up shots.
I'm no stranger to recoil. I've shot revolvers in 45-70, .460 and .500 S&W. But I don't like the J frames in .357 made of Scandium. With such small grips and weighing 11.4 oz's by the third round I find I have to adjust my grip. This is not something I want to do with a defensive pistol. In .38 they are manageable. I know that it may just be psychological but I always feel a little undergunned with a 5 shot. That 6th shot is a 20% increase and maybe it's just a larger gun with a longer barrel that make me feel more confident. But don't listen to me the only way you will find out is to rent the gun or use a friends and find out for yourself.
I went to the S&W and Ruger websites and couldn't find a revolver I would want to carry or advise to someone. I would be looking at used guns with no key lock on it.