I referred a while back to Matthaeus Gesner’s opinion, delivered in 1787, as to why chapter divisions were not authentic. Diana Albino gives him as her first reference on why there is a habit of treating such things as inauthentic.
Prior to his chapter 21, which I translated there, he makes the following remarks:
Commode hic nobis accidit, & commodius multo lectoribus accidet, illa capitum quae vocantur & titulorum in minora segmenta divisio, iam a Schoettgenio instituta, quae etiam ad parallelismum, quem vocant, indicandum, unum optimum interpretandi libros quoscunque instrumentum, apprime utilis est, ut mirer, rem ita facilem, & olim cognitam, negligi fere in splendidis librorum antiquorum editionibus, praesertim cum metus non sit, ne ea similia bonis libris vulnera infligat, qualibus capitum illa divisio occasionem dedit.
XX. Hic locus est plura de infelici illa capitum divisione, conjunctis ei rei lemmatibus disputandi; qua de re visum est hic uno loco ita dicere, ut totam complecti aliquis animo possit, ac tum in his, tum in aliis libris eorum, quae hic disputata sunt, meminisse. Jam ipsos antiquos scriptores uno fere tenore & continuatione libros scripsisse, satis constat, ut non tantum historias in unum perpetuum & undique cohaerens corpus redigerent, sed ea etiam, quae diversitatem aliquam habent, arte quadam inter se devincirent, latentibus, ut in Corinthia columna, membrorum finibus, aut in statuarii opere commissuris, & subtiliter permixtis, velut in pictura extremis partis cujusque lineis. Cujus rei nescio an clarius & mirabilius exemplum exstet Ovidiano Metamorphoseon opere: quod qui uno quasi spiritu legere volet, ille demum poetae ingenium mirabitur, qui mille partes dissimillimas ita inter se coagmentaverit, ut uno solido factum marmore totum illud templum videatur. Ita quam apte Plinius ille naturae historicus transitione res saepe diversissimas connectit? ut unum voluisse illum librum uno quasi protelo percurrere appareat. Quae cum ita sint, dissecuisse antiquos, quae scripsissent, in partes libris ipsis minores, non est probabile: qui librorum ipsam divisionem ad voluminum & chartarum modum necessitate quadam attemperaverint.
Well, quite so. He argues that ancient books are all written in a single piece to join together diverse materials, like a Corinthian column, and even Pliny the Elder in his Natural History does the same.
Of which I do not know whether a clearer and more admirable example exists than the Ovidian work Metamorphoses: because he who chooses to read it as if in one spirit, he will marvel at the ingenuity of the poet, who has joined together a thousand utterly dissimilar pieces in such a way, that it seems made like a temple out of one solid marble. So Pliny, the historian of nature, often joins together the most diverse materials by an appropriate transition, so that it appears that he wanted to run through that one book as if in one go. This being so, it is not probable that the ancients divided, what they had written, into smaller parts than the books themselves, when that division into books was only forced on them by the necessity of the medium of rolls and papyrus.
Unless I am quite misunderstanding the argument, this is merely a subjective opinion.