The island analogy's misleading crap. A couple tweaks to make it closer to reality (say, if the islanders had been working for
millennia and we only cared about a handful of their very best works from that entire time span—instantly less crazy with just that one tweak, no?) and it falls apart. There's almost a hint of an interesting line of argument, buried somewhere in there, but the way it's presented isn't good and is the precise opposite of convincing, on close inspection.
Relying heavily on really bad analogies seems to be a theme in the paper, reading on. There's some hilariously-bad question-begging-laundered-through-analogy in the bit about body-building advice / reasons-to-study-historical-philosophy.
Leading with emphasizing the importance of correctness is also pretty silly when we spend much of a student's training for most other fields teaching them one useful lie or another. That philosophy's lies happen to often come from very old books hardly seems material. Clearly, scaffolding with outright known lies is the norm, so "much of the material is probably wrong" isn't, per se, much of an attack.
I don't think the paper's conclusion's even necessarily wrong (and by calling for some vague "less" focus on the history of philosophy, it defies firm refutation anyway) and some of it does make interesting points, but damn, it's got some seriously off-putting flaws. I especially think it fails to make a strong case against such study as training for philosophers. But maybe there are far more doctors of philosophy out there who spend their careers analyzing historical philosophy, than would be optimal. That seems plausible, but also doesn't seem to be the focus of the paper.