hmm colossus has gotten massive strength over the years , and yes he is "just" steel , but it is and incredibly strong organic compound that resembles living steel, and is actually harder than most other metals , adamantium carbonadium and vibranium not withstanding. AND people tend to forget colossus is a fairly good martial artist with plenty of experience and is fairly smart, not just your average big dumb smashing machine.
so colossus...