This is a v. interesting paper.

On my first reading of it, I found section 1 on Imam al-Shafiʿi's presentation of the usul of some of the Hanafi imams regarding the mursal to be strong.

His many statements from some of the imams on the issue are not only explicit but... https://twitter.com/Al3uny/status/1320795747273609216

... also constitute a direct, contemporaneous, & trustworthy source from them, which is unique.

How much weight should it be given noting that al-Shafiʿi was their opponent? Readers can decide but given the number of times al-Shafiʿi relates this view directly from them plus...

... al-Shafiʿi expressing some critical awareness of how he is presenting & wording some of these exchanges he is having with some of the Hanafi imams makes it a source that cannot be easily dismissed.

I found Section 3 on al-Tahawi to also be reasonably well-argued, though...

... an expert on al-Tahawi would have to see if there is anything in al-Tahawi's works to challenge or complicate the quotes Sh. Hatim has brought, some of which are explicit on the issue.

Finally, Section 2 was one I found to be least convincing. It relates to quotes in Abu Yusuf's texts demonstrating he didn't accept mursal as proof (independently). However, most of the quotes concern Abu Yusuf rejecting arguments that appealed to amal.

Is this the same as mursal? Or does the reasoning underpinning Abu Yusuf's rejection of the amal-argument made by the likes of al-Awzaʿi also extend to the mursal? I'm not convinced at this point that it does.

(FYI: Imam Muhammad also attacks amal in his texts)

Also: I did not summarise the actual arguments in this thread because people should just read the paper if they are interested in it or want to comment on its content. It is not very long.