Thanks for the excellent cross-referencing on Brahma Sahampati.
It is interesting to note that in the suttas you quote, he "confirms" the teaching in question with a "So it is, Blessed One! So it is, Fortunate One!" refrain but he does not do so in SN 6:1.
There could be reasons put forward pertaining to the depth of the teaching of dependent origination, but it seems more plausible that at the time in question Brahma Sahampati didn't know that "so it is", because the Buddha had yet to teach Dhamma. Therefore, he had no basis upon which to proclaim ""So it is, Blessed One!"
"Do not force others, including children, by any means whatsoever, to adopt your views, whether by authority, threat, money, propaganda, or even education." - Ven. Thich Nhat Hanh
"The uprooting of identity is seen by the noble ones as pleasurable; but this contradicts what the whole world sees." (Snp 3.12)
"To argue with a person who has renounced the use of reason is like administering medicine to the dead" - Thomas Paine