I did mean 10. I guess I got my later FF games a little mixed up, mainly because I haven't play4ed any of them past 9.
(I also haven't played 8, and the most recent one I've actually completed is 6.)
Yeah 10 is good but I think 10 no sphere grid, no aeons, etc just becomes Rikku and Mix spam to beat the game since you can do crazy things like trio of 9999 to guarantee 9999 damage and healing although dealing with aeo attacks is probably very difficult, especially since certain skills will be unavailable to you.
These are also two different types of games (action vs RPG) so they are quite different in that respect as well. Action is probably harder since you need to react and cant plan out like X.
If you think NSG is too easy for that reason, try NSGNSNTQ:
* No using the Sphere Grid
* No summons (except the few times when the game forces you to)
* No Trio Quartet (no using Quartet of 9 or Trio of 9999)
This challenge means that you can't just use Mix to guarantee 9999 damage.
(If you want, you could just ban overdrives entirely, which would also prevent Mix use.)
One other difference between action and RPG: In action, it is, in principle, possible to beat the game at starting stats just by being really good at dodgind and having endless patience (there are a few exceptions, like Crystalis and Ys 2, where being too underleveled can result in you being unable to damage the boss in the first place). In RPG, this may not be possible, as you can't just dodge out of the way, and therefore need to take hits; in cases like FF5 and FF10, it's not entirely obvious that such a feat is possible.
In Dragon Warrior 1, for example, it is not possible to beat the game at too low a level:
* At level 6 or below it's outright impossible. You have no way to avoid the final boss's attacks, will die in one hit, your normal attack will do at most 1 damage, and the HURT spell, even if you get it to work (1/16 chance), is not going to do nearly enough damage.
* At level 7, it is theoretically possible, but is simply not going to happen without RNG manipulation. During the final battle, you need to put the boss to sleep (1/16 chance), then each round, you need to cast HURT, have it work (1/16 chance), hope you get a good damage roll (if not, you might not have enough MP to finish the fight), and then there's a 1/3 chance of the boss waking up and killing you, and you can't have that happen.
* Through level 16, the situation is the same. You might be able to get away with *slightly* less luck, but still don't expect to win in this situation.
* At level 17, you get HEALMORE, and now winning is reasonably possible, though apparently you still have to put the boss to sleep once (again, 1/16 chance), and the boss waking up right away could be a problem.
* Level 18, your stats have increased enough that you can kill the boss with normal luck, and without needing to hit any 1/16 chances.
* Level 20, you're likely to win if you avoid using MP on the way down. At hlgher levels, the final boss eventually becomes really easy (but be aware that Red Dragons could still kill you if you're unlucky; I believe I got killed by one at level 29, and the cap is 30.)