I don't know why you excluded PhDs but their code aren't any better necessarily. Hiring straight from school doesn't necessarily mean bad S/W engineering skills. But generally the research code is either made hastily during exploration or by people not having enough Software Engineering background.

Many research scientist I've seen at large tech companies don't have good CS background and write code that's either unreadable, unscalable, unmaintainable, or buggy at times. They often have good ideas but don't do much software design.

Having been both at infrastructure teams and research teams, there are certain individuals in research orgs joining straight from school who think they are responsible with coming with a new and sexy thing and other engineers are responsible to run in production. It's like computing eigenvectors in Matlab or Python over a toy dataset and thinking you've done the bulk of the work of computing PageRank in production and should receive all the credit for a full search engine.

That attitude is a red flag to me.