but all those buildings are up to code now too right? And the fact that people keep them occupied for so long and renovate speaks to their intrinsic quality I'd think.

but tbh - quality is somewhat a red herring. Today, quality is all because there is caulk (greatest invention), plumbing, and longer lasting paint. Yesteryear, quality was because they used all natural materials which are unaffordable now. Either way, keep a house dry and occupied, and it will stand for centuries, regardless of when it was built.