Yitay, off-hand, the Trumos HaDeshen was saying that covering all hair is de’rabbonon, not that the whole thing is derabbonon.
I do not have time to read your whole megilla, say it shortly. From what I did read, it looks like your opinion is not shared by the regular Poskim. Chofets Chaim held it was de’Oraysa. That’s the pashtus of the sugya.
Do not give me this MO schtik: going into the sugya, finding one shvere da’as yehid or a minority opinion and relying on it. Like you tried to do about the pritsusdik clothing — using the shita that it all goes basar the minhag. Most Poskim do not hold like that and it does not fit the metsius.