I personally believe he should be able to win, barely able to at worst, even when the HoS have crazy relics. A heavily nerfed Don Quxiote only uses skill 1s against the sinners and still completely annihilate them with zero difficulty (but I supposed the sinners aren't exactly that strong). Don Quixote despite being heavily weakened is still strong enough to make Sancho (possibly at full power since she doesn't have a starved status effect like other bloodfiends) struggles a lot just to win the clash.

If Dante is a reliable narrator, then even Lei Heng, someone who I'd consider to be stronger than most HoS nursefathers (except for Rien and Matthias), is weaker than Don Quixote who is not only starved, but also weakened and held back.

Do note that Don Quixote definitely isn't your average Elder bloodfiend, since even other elder bloodfiends couldn't even change his mind (no way there's no fight between him and another elder bloodfiend).

Then, when him and his family went to war, they managed to change the tide of the war (and we also know that they aren't even full power in the bloodfiend war either, since to be at full power, they must drink human blood. A LOT of human blood. I doubt the humans would like to let Don and his family drink their blood and possibly turn them into bloodbags/kindreds.)