A buggy big ball of mud that does mostly the right thing is still going to beat a high-quality, carefully architected solution that reliably does the wrong thing, though.

And for a huge amount of code, it's not very hard to make it good enough, because the requirements, once understood, are pretty straightforward and perfect correctness often matters much less than you would think.

"carefully architected solution" is not what they are saying. A "buggy big ball of mud" will not generally "do the right thing", if it did, it would not be a "buggy big ball of mud". Straightforward requirements do not imply straightforward solutions. In the early 2000s Facebook wanted a quick way to search for friends updates, a straightforward requirement. Turned out they had to build a full graph DB inside MySQL, not straightforward code at all.