Is it? Generally, when someone has gone to the trouble of building up the necessary muscle to lift 1 ton (I know the record is closer to half a ton, but humor me), they haven't spent much time on training their body how to fight, and therefore wouldn't be able to generate the same power to muscle ratio as someone who spent their time training to fight instead of lifting weights. Even with something as simple as punching, technique makes a huge difference in how powerful the punch is. Could the musclebound contestant punch just as hard as the one that has trained? Probably, but it isn't going to be the full 3-4 times his lifting strength due to his lack of technique. Put simply, he doesn't know how to use his muscles to achieve the best punching results, he just knows how to use them to pick things up.

So the rationalization behind it is that there has to be a trade-off. You can't have one fighter who can both lift 1 ton and also employ advanced combat training in order to utilize all that muscle to its fullest advantage, simply because he would be able to steamroll any other character in that tier (unless all characters could do it, but then there's no point to unique and diverse characters).