What do you find so hard about Zelda 2? What enemies are you having trouble with? I don't put it up there with games like Ghosts N Goblins and Ninja Gaiden for difficulty. The only really hard parts I can remember are Death Mountain and the last palace.
Maybe I haven't given it a fair shot, but the enemies require such precision that it feels like a chore even if I could perfect a strategy. The Iron Knuckles (?), the Axe Throwing Enemies, the Boomerang Throwing ones, the Skeletons - they seem to rely on tiny precise hitboxes while you certainly aren't so hard to hit. The game seems to expect me to do split-second shield positioning based on tiny information, which is fine for a boss or something but quickly feels like it would be a hassle even if I really dedicated myself to it?
Then you get slow-moving but tedious to handle enemies like the fireball spewing heads and it just cements itself - it tolerates only very little mistakes.
The level-up system isn't even for feeling powerful, it's to keep up with the crap the game keeps throwing at you non-stop.