Rhino had several bouts of chemical and radioactive enhancement before they strapped him into the costume, he has powers without it. He's just way tougher and has a giant horn wearing it. He's had a couple of other power-ups over the years, he had a brace of gamma treatments when he briefly became a Hulk villain, there was a very brief period where he had another neew bout of treatments and a brand new cybernetic suit of armor, Hulk kicked his ass and it was never seen again.
Even with all that experimentation though he's still a league or two below Juggernaut's tier. Cyttorak is that OP. Still, it doesn;t really matter. They're both effectively treated the same because they're both retarded bank robbers, Juggsy just brings home a bigger paycheck.