I don't... quite understand, why would anyone put an item in JEI just to say its no longer in the mod, instead of just... not putting in the mod, which is what they did. As mods update, you can't just assume all the same stuff will be in there, they are constantly changing and evolving.
As for the quest book, do you mean you expect them to direct you towards a source of flight instead of them expecting you to work it out for yourself?
I know the Air Sigil is a form of flight available - it might not be jetpack flight, but it is something.
EDIT: something that genuinely IS aggravating is that because its only on the FTB app and not Curseforge, it makes looking up what mods are in the pack difficult (possibly impossible?) without downloading it, or at least downloading the FTB App. Which feels... off.