> Scientific papers usually aren’t written as debate transcripts.
Sure they are, although a debate wouldn't be contained in one paper written collaboratively by debating authors, as you seem to imagine -- it would play out over a series of papers, each of which cites previous papers and claims they're wrong.
For example, Timm 1989[1] argues that modern Breton is a VSO language, disputing the claims of Varin 1979[2], who claims it is SVO, which in turn disputes the traditional understanding that it is indeed VSO.
Or the famous paper of Haspelmath 2011[3] citing many other authors' proposed approaches to word segmentation and arguing that they're all wrong (i.e., that "word" is not a meaningfully defined concept in linguistics).
Where are the papers that you claim exist about the lines between languages? If this is really something mainstream linguists care about, you should be able to give examples in non-fringe journals.
I just checked the citations on the Wikipedia article for Middle English like you suggested, and found zero papers about whether Middle English should be considered "the same language" as modern English. Can you tell me which ones specifically you mean?
[1]: Timm, L. (1989). "Word Order in 20th Century Breton". Natural Language & Linguistic Theory, Vol. 7, No. 3, Special Celtic Issue, pp. 361-378 (https://sci-hub.tw/10.2307/4047723)
[2]: Varin, A. (1979). "VSO and SVO Order in Breton". Archivum Linguisticum 10, pp. 83-101
[3]: Haspelmath, M. (2011). The indeterminacy of word segmentation and the nature of morphology and syntax. Folia Linguistica, 45(1). (https://sci-hub.tw/https://doi.org/10.1515/flin.2011.002)