Page 24 of the free pdf sums the whole paper:

We believe there are two main reasons why mediaeval Poland is less inspiring than the PLC to contemporary Polish creatives, both related to the search for an appropriate heritage for the post-1989 Poland. In 1989 Poland abandoned the USSR-dominated Soviet Bloc to embrace Western democracy and capitalism, so it was in need of a new heritage to replace the (post- )Soviet legacy – but it also searched for some degree of its own national identity defined against the universalising pan-European narrative. The Catholic feudalism of mediaeval Poland could not help much, built as it was under German and Czech influence within an analogical panEuropean universalism. The (arguably) exceptional Polish–Lithuanian Commonwealth provides an alternative point of reference, distinguishing Poland from both Eastern and Western neighbours. In the discursive construction of heritage and memory, the PLC heritage was a working solution for nationalist EU-sceptics and multiculturalist EU-enthusiasts alike: the former variant interprets the PLC as an imperial Polish conservative Catholic project, the latter as a joint Polish–Lithuanian–Belarusian–Ukrainian project of an EU-like commonwealth of many cultures and faiths (more about it in Mochocki, Schreiber & Majewski, forthcoming-b). The second reason why the PLC is a more “productive” heritage than mediaeval Poland is its political system: the republican character of its parliamentarism, elective monarchy, and civil liberties is much more relatable for the 20-/21st-century parliamentary democracy than mediaeval dynastic monarchies.