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To respond to your list:
1. No specific concept, gets used all the time in fantasy stuff.
2. That’s hardly a similarity. That a character (of a certain class) joins and leaves again. O_o
3. Considering Square’s history, that might have been a wanted reference.
4-7. See 1.
8. Almost every final battle in a JRPG is in one of those 2 locations. Besides this; considering they’re completely different locations, they can’t be called similiarities. <_<
9. That I’ll definitely give you.
10-11. Most likely a wanted reference.
12. They uh… are of foreign culture and wear masks?
13-17. See 1.
Basically, all similarities you list are either general fantasy clichees, JRPG clichees, no similarity at all, or most likely wanted references (considering how FF games reference each other all the time).
So basically just your #9 is a kinda valid point. But it also could be just a coincidence.
Hence, odd numbered FF games all featured nameless generic characters which were identified simply by their Job class. Naturally, each game of this particular group used the Job system as well, in FFI (in a very embryonic form), III and V (I’m not counting the DS remake of FFIII though in this example – even though the addition of named characters in lieu of the ‘Onion Kids’ didn’t really change anything, as from a narrative standpoint they were little more than fancy wallpapers taped over the NES generics anyway.)
FFII, IV and VI however featured a group of named characters with specific abilities and skills, each with their own individual back stories too, covered in varying degrees of detail. Often parties weren’t static in these games, with different party members coming and going at random intervals, before finally settling down as ‘static’ towards the end of the game.
This all changed with FFVII though, as the development team abandoned these traditions in favour of a more individual focused style of game. Each successive FF game was unique in terms of battle/ability system, although story based, named characters became the norm (only FF Tactics and Tactics Advance I and II once again featured generics, although I suppose FFXI does as well ;)).