It wasn't quite as bad in Nighthold itself vs. Trial of Valor if I recall correctly. For ToV you HAD to have that 5% bonus damage trait on all your DPS to make it past Guarm and certainly for Helya (though that was much heavier on composition/mechanics, it still required a lot of numbers.)
I don't remember Nighthold being as bad; but I might be forgetting. The bump needed for Tomb of Sargeras was also somewhat significant, but AP acquisition was smoothed out by then more or less, and as long as you had all the Legionfall traits unlocked you were okay, though obviously each level beyond would help a little bit collectively over a whole raid team.
Legendaries were a massive factor throughout all of this time, but if you had the fortune of not needing to switch specs or classes altogether, then there was a decent chance you could have had everything or most everything by the time Tomb progression was heating up if you played a decent amount.
For people that did switch or were extremely unlucky, well, it wasn't so good.