Has anyone looked at Bronzor yet? It beats Bronzong by 13 base points in both defenses and only loses 10 base HP (so it has 57/129/129). It could make up for it's pitiful attack stats with Toxic-stalling if something stays in and Level Ground to keep sweepers at bay. It can also set up screens, weather, or Trick Room (obviously). Hypnosis, Safeguard, and Heal Block are at least worth noting too.
It gets completely walled by anything immune to Poison and if something doesn't care about the speed drop it can stay in anyway. So Poison Heal Gliscor, Reuniclus, Skarmory, Nattorei, and Crobat will force switches, but it can definitely come in and absorb basically any hit, and in a lot of cases it can screw over sweepers if they don't switch.
Whenever you think about a pokemon's prevo with weaker stats, think about it first:
would you actually use its evolution in the first place?
To answer that, Bronzong sucks (ignoring offensive TR, which I've never found to be too good); why would you want to use bronzor?