I am unsure in what time Folly's fictional speech ought to be placed
All the verbs in this paragraph are present tense (Britanni sibi vindicent, Scoti sibi blandiantur, Galli sibi sumant, ...
), so I think it's pretty clear Erasmus aka Folly is talking about the contemporary claims of contemporary states/peoples, which is why Hylander correctly added the qualifier "[modern]". And I think Erasmus/Folly probably concedes there is a historical germ of truth to these claims** but is poking fun at how, as he says, nature seems to have planted Philautia [Self-Love] in nations and peoples, not just individuals (Iam vero video naturam, ut singulis mortalibus suam, ita singulis nationibus ac pene civitatibus communem quandam insevisse Philautiam atque hinc fieri, ut Britanni ...
As to auctores
, you're clearly doing a deep read, and I get the impression you're intentionally and admirably and correctly trying to work out your own understanding of each sentence without resorting to a translation. But let me cheat and quote Adams' translation: "The Greeks boast they have invented the arts, ...".
As I understood, Folly was mocking not the ancient Greek heroes,
I'll just note again that, per the Amsterdam-edition citations I noted above, Erasmus means by "heroes" not the likes of Heracles or Theseus, but the giants of literature and philosophy, like Plato and Aristotle. (I'm not saying you disagree with that.)
** As I'm learning looking at the introduction in the Amsterdam edition, Erasmus anticipated and indeed received the accusation of impiety, first in a letter to himself from one Martin Dorp. I hope it is the Martin Dorps who rot in hell, as I can't abide people who lack all sense of irony
. Anyway, this charge was answered in part by Erasmus himself in a letter back to Dorp (dated 1515) and in part in a 1515 commentary to Praise of Folly by a Gerardus Listrius
. As quoted in the Amsterdam edition, here is Listrius' comment on Britanni ... mensas
in chapter 43 (the underlines are mine): Vide lector ut rem per se mordacem festiviter, et citra morsum
tractat. Quis nescit, ut singulis hominibus, ita et singulis nationibus sua quaedam vitia esse, de quibus vulgus etiam sua habet proverbia
. At hic nihil attingit odiosum, sed tantum ridicula quaedam commemorat, ut intelligas illum candido illo Mercurii sale ludere
voluisse. Nam Britannos etiam laudavit, si vindicant sibi, quod et habent, et habere pulchrum est