User blog comment:Crimson and Darkness/Volume 24 discussion blog/@comment-26926813-20171118100132/@comment-29963364-20171119081453

Don't forget that Vasco faced the entire Gremory Peerage (+ Arthur) on his own, and only lost because he ran out of stamina due to his age (he's 87, yet he punches like Sairaorg).

It wasn't just his raw power that enabled him to do this. He also has almost 9 decades worth of battle experience & knowledge against supernatural beings (mostly Devils & Fallen Angels). He even completely nullified Rossweisse's magic by just poking it in certain places with one finger, and dissed her magic saying her magic is so easy to unravel.

Now, take all of that, and put Vasco in his prime (which seems to be when he's 50, according to the spoilers). His physical strength, durability and speed are at their peak, and he has "stamina for days." And he has the Durandal 2 (an upgraded version of the Original Durandal) and a second Red Sword (we don't know what it's called yet, but we assume it's just as good as other Holy Swords).

Based on just his physical abilities & skills, I'd say that you'd have to be at least Satan-Class to be a challenge to Vasco (Prime). But since Vasco has his 87 years worth of battle experience on top of that, it's not unrealistic for Vasco to be able to handle Fenrir (Nerfed), Bikou and Vali (EJOD) all at once.