superficial, and to be fair to ST they do call it a research brief, but very interesting. Thanks to the OP for posting the link. Hopefully ST will follow through with a proper study.
As DCs can apply to up to 5 Uni's, and with the same PS needing to cover all 5 - with the odd exception, it would have been useful if their initial research in terms of teacher and admission tutor view of the same PS could have featured the response from admission tutors from five highly selective universities to compare how consistent or not these were too.
I'd certainly go with their opening recommendation. Universities should be more transparent about how specific subject departments use and evaluate personal statements. This information should be shared widely, and effectively, with applicants, schools and teachers When DS1 was applying a few years back the steer from the subject admissions tutor at one highly selective uni's open day was substantially different to the PS guidance on the uni's own website.
All that said, and obviously not covered by this specific report, an even bigger issue is that there is a whole chunk of schools where no DCs are even applying for a course at our elite universities. Those schools, and there are an awful lot of them, are easy to identify from the data that both Oxford and Cambridge publish. and I fear the list would not be that different for the likes of Imperial, LSE, Durham, Warwick, UCL, or pretty much any medical course.