I ran across some developers (in multiple orgs over the years) that would produce large amount of almost purposefully unmaintainable code. Yes, they were “productive”, and no, the stuff they produced made no difference and was a waste (both features wise and code wise since). 100% of these codebases turned out to be unsalvageable and were rewritten. It just would usually take orgs many months, usually after such developers leave to realize the complete and utter waste they left.
Not saying there are no slackers, it’s just productive devs are not necessarily those that produce the most of code.