Hard to say. Bugs will definitely cut your yields. Pk 13/14 and things like potassium sulfate aren’t complete nutrient packages, so maybe that had something to do with it. But just a guess. If it was journaled start to finish with pictures and data posted I could probably provide a lot of feedback. But without anything to go with, I would be guessing.
A 4x4 with a 600 is capable of producing 1-2 pounds in the right hands. Imo if plant size is consistent, there’s not a huge difference between a low yielding strain and high yielding strain. 10-15% maybe. But an unhealthy improperly cared for plant could potentially be a huge difference.
These plants were underfed and hermed for example, not going to get best yields that way.