I am one who believes
That loading with the lever with the pistol still assembled puts more stress on the pistol than one might think.
If you calculate the mechanical advantage of the lever (In most pistols it is about 9) Multiply that by the force needed to get the ball seated and the stress on the frame can be two hundred pounds.
I know...I know.... These pistols were designed to be loaded using the lever. About a billion pistols were made and used successfully in battle without the benefit of a loading press. There are likely very few examples of steel frame revolvers coming apart during the loading process. (Maybe a higher population of brass frame revolvers).
I agree that the revolver undergoes a good bit more stress during firing than during loading. My thought, though is; If you have a press and are permitted by the event or range rules to use it, Why not use it?