I am not quite sure about the op's comments. I made a Tyria Ele and brought him to NF and played til Vabbi then went back to Tyria to Herohench almost all of the missions including THK which was a piece of cake, since all i did was to camp at the king. Not forgeting that now you can actually get the hencies/heros to move to certain locations or stay back for tactical purpose, i should think it would be easier with Heros from Nightfall.
However if the OP was a new player to GW as a whole and having played NF (a more compact game) for some time then moving to Tyria (long and stretched out game), i could perhaps see why it may be percieved as more "difficult". But having said that, most things when new are always more often than not difficult in one way or the other.
Hard adjusting to old Guild Wars from Nightfall
Thallandor