I wouldn't pay too much attention to answers from this respectable subreddit when they express more what is a historiographic opinion than a fact. And when at the same time they are fighting strawmen.

The European Dark Ages narrative was indeed overblown and needed correction. But this correction went too far. It seems to be now at the stage of explicit and vigorous denial of any downfall of fortune in the Western ex-Roman provinces. I'd posit that such a denial is even more overblown than the initial myth it aimed to correct.

I can offer you a link to an author arguing for this position: https://slatestarcodex.com/2017/10/15/were-there-dark-ages/

I understand the point and personally regard "the dark ages" (500 - 1,000 CE) as a period lacking in scrolls, commentary, and stonework compared to the Roman Empire .. but largely life as it was for those that were never an integral part of the Roman Empire workings .. eg: those that delivered food to the Romans in the UK never wrote or built much in stone themselves and once the empire faded in half to the east they carried on without record.

Regardless, your link is an interesting argument that doesn't provide anything especially compelling to the contrary .. a void, here a void in the record, is easily filled with speculation.