It was the Suit that took a lot of the damage hense the armor. It wasn't lack of Sunlight he just wasn't as invulnerable as his previous self was. Strong yes but not as invulnerable kinda like Mr. Incredible. Mr. Incredible is strong but can be hurt if you can get past his suit which if going by the demo Edna gave Helen must be made of f-ing vibranium. It protects his hands when he hits something cause with his strength and no natural invulnerabilty would hurt or cause injury to himself. Incredible I think had Wonder Woman level durability. If you put her in Clark's armor suit she'd be a Tank just like Bob is with his supersuit on. So I think Morrison intended Superman to be at Golden Age level with out the Suit on and Silver Age with it on. The desciption for it even said it helped metabolize solar radiation better making him stronger and it kept him from losing as much energy in red sun conditions. But it had a collar so it was trash. Boohoo.