See p31:

Text as written, what I described is exactly what it talks about right here in this section. Being outnumbered is an exceptional circumstance, being significantly out-weapon and is a significant circumstance. I may have extended the degree of that significant circumstance by a second full level, but some of the examples later do that as well, so that also counts as text is written.

While you would be technically correct that advantage and disadvantage "don't have any effect on the threat Level," the actual mechanical impact is exactly the same as changing the threat Level insofar as the GM is concerned. There are three moving possibilities that the GM can choose from to represent the impact of the situation.

• Change the target number between 7/8.

• Force/allow one reroll (a half Level).

• Force/allow to rerolls (a full Level).

Any adjustment beyond that is apparently fairly explicitly leaned against in the text; there you are right.

The big crime here is that this stuff is buried in a section that looks exactly like all of the other text talking about casting lots when in any better designed and laid out game, this would be in one of those really bright sidebars with multiple arrows pointing at it saying "this is important." Because it's huge. It's also not called out in the GM section anywhere, even though that would be a fine place to point out "here is your primary mechanical tool for having the narrative world impact the mechanical world of the players." Along with a nice casual list of various things that might bump up difficulty or provide advantage to the players where they could stick in some more weird.

The mechanics aren't complicated and they aren't bad, necessarily – but they aren't better than the ones that they had nor are they more narrative (despite the claim at the beginning of the book), and it all seems so unnecessary.

Really, this section should have simply been about setting a Level for the opposition, as an aggregate or as individuals, and then let the already defined Level interaction mechanics do the heavy lifting. It almost feels as if that was the original intent, given the rest of the layout around the section, but it fell on the floor at some point.