Endurance has no effect.
It is possible to reach max flight time with enough drugs, stats
Lets be honest here. There is no power armor build. Power armor doesn't give you anything new (apart from jetpack) it only compensates for possible flaws.
I hated the jetpack my first time I got one. On my second game I boosted my AGI to 11 and used AP bonuses and it was freaking sweet as hell ,jumping up on to the second floors and over houses( I did break my game once going up an elevator shaft in the old airport to a place that isn't supposed to be accessible till the brotherhood show up).
+edit - on that note the game wasn't really built with jetpack in mind i broke so many quest starts getting to places early...like flying into diamond city from above before going to the front gate.
~tgm
It's useful for getting on top of buildings and cliffs, well small buildings and cliffs, but it's not completely useless.
You can gain some actual air with burst use of the Jetpack, i have climbed quite a few buildings in the Center of Boston in the game, even before i got my AP really high.
But like others have said use mods if you really want to play with the Jetack and feel like you are Tony Stark in an iron man suit.