I posted this earlier.
That doesn't cut it at all. The argument isn't that he picked up the house so he should have enough strength to break the chains. Its just an example of his strength from a long time ago. Later he does push-ups on his index fingers while supporting 8000 pounds on his legs. That is an absurdly high pressure level on his fingertips. First example he was bleeding profusely the second he was still suffering from Luffy's damage.The means we have no idea what is Zoro's upper level of strength are except its easily in the 10s of thousands of pounds before the TS. He should be drastically stronger now. Steel is very hard to break a steel chain even in real life but the little hints of Zoro strength put him above whats needed to accomplish he task. The best example we have of Zoro's strength comes from Luffy pushing two buildings apart in W7. He split the buildings foundations with no leverage. That is a way more monumental task breaking steel chains and is a similar action.