I hope you have time to review one more reply before you finalize your decision. I've played NIN since it came out, albeit i skipped HS but the remainder of ARR and now SB I've continued to main the job. I've always been under the impression that the only people who choose to play this class are the ones that were a bit of perfectionist. Perhaps it's only me I spend a lot of time in practice groups helping others clear content while learning to optimize my runs. Most other NINs I've run into seem to have the same thought process as well. I don't know if the general mechanics shy many players away, it is an aesthetically pleasing job so I don't know why people would stay away from it other then it's initial "difficulty level" people gave it from the start.
Now what the statistics do not show you, is the how landing or missing TA effects you and the group. Landing your TA increases the raids dps so there is no way to measure the highest dps - lowest dps for specifically ninjas in a fight. The only honest way to measure a classes' difficulty is perhaps fflogs cast per minute (CPM) measurement. You'll have to go through each fight and see the average CPM between NIN and other classes. I think you'll find the numbers you are looking for. I'll list one example I found:
One of the top end fights for Neo-Exdeath for one group shows:
SMN at 5k dps with 36.1 CPM
NIN at 4.5k dps with 44 CPM
Found similar numbers for NIN/MNK comparison.
So in conclusion that ninja is performing 8 more actions per minute then that summoner and is doing 500 less dps. The fact is our combos are more forgiving on direction because of all of the other things we do in fights typically. Our gap closer shukuchi itself is a skill shot, you can't just target a mob and teleport to it. Don't get me started on mudras, you fail it or accidentally press it twice you're done for the next 20 seconds, say bye bye to your dps. I play NIN and MNK both I find monk to be harder atm but that is because i'm still new to it and learning. They are both fun classes and I would recommend both. I hope this helps you to make an informed decision.