I personally play both Ninja and Monk,

My personal opinion? Monk is a lot less worries than Ninja, really, and Ninja feels like it throws their enemies with everything (even their shoes)
Have you seen their opening? Its a hell of a lot of things to throw out.

Positional in my opinion isn't that difficult, really, if anything the single positional Ninja has gives a lot more stress than any Monk's positional, since you only have one shot every 60 seconds.

MAYBE the main reason as of why I find Monk a lot easer than Ninja is simply because I play with controller. I do imagine that playing with keyboard while locking on target would imply a lot more difficulty.

I mean, as a PC player I have got the chance to play melees with keyboard, and I've hated it to no end, but with a controller this becomes so easy...

So for a player with a controller it might be a tad more difficult to deal with Ninja than Monk because of the extra attention on the ninjutsu rotation and gimps, and for a keyboard player it might be easer to play with a Ninja than a Monk because of the quantity of shortcuts available and less movement stress...