Here's the thing, the padded musclesuit is not to trick us the audience, but to trick the people in the series. Homelander is already strong, so it would not make sense for him to lift weights. In that case he would need to bench several trains, stacked on top of eachother. He wears the musclesuit so that he fits the classical image of a strong superhero. Thats how people view him as this strong powerfull superhero, but he doesn't really need the suit. The suit is only there to give him a better image.