The Wither is so much harder because of its persistence to wither poison you or something and makes you blind and everything. It's just terrible to fight a wither
Wither is better because it can just poison the dragon then the dragon won't be able to fly!!!!!
Well you see, the ender dragon lives in the End, which is a ask in itself to get to. and it also flies super fast. The ender dragon is super hard to kill because of how high it flies and how much health it has. Not to mention the endermen and the health regen towers. The dragon is a pain in the butt.