There's so much I could say about the crap I found (and if someone asks I'll be happy to!), but I can summarize it by saying that it was bad even compared to the what I've come to expect from WP sites that are plugin- and WYSIWYG-layout-builder-laden, to the point of being utterly unmanageable from the WP backend interface, even on a local setup, because just exploring the ridiculous custom interface pages take ages to load.

I truly cannot imagine this code being written by anyone but a lowly, unsupervised intern at this company. And yet, based on my experience, it was probably just some 'regular' employee, unnoticed by his manager, and his manager, and the client none the wiser because how should he be able to assess competence.

That being said, if they weren't trying to eke every microsecond of performance out of the system, then that's pretty poor design, maintainability wise.

She wasn't trying to eke every microsecond. There were some smart guys on our team, and we were all afraid of that code! The programmer who wrote it would fire back about her Mathematics PhD if you ever tried to bring up Object Oriented design. When I was there, she would sit in the cafe downstairs eating a sandwich, until something broke. She wrote herself fantastic job security!