Based on:
1.Availability, they can be recruited earlier
2.Stats
3.Rune slots, their rune slots start opening at a lower level
4.Those powerful runes become available, you can actually farm/get them

Then we can tell people when to change their party and use more powerful characters

i think if the story sections can be laid out first with what items are easily obtainable this will be a lot easier

To make one ranking is already hard work, i don't think anyone would commit to make numerous rankings for several points of game. I'm willing to evaluate characters at their lv 60 which means at late game stage though.

By the way... you didn't mention unites your criteria, in term of effectiveness, unites are dmg modifiers and i wonder why people always tend to ignore it? Because it takes more party slots so they can't use all their favorite characters, perhaps? I'll test soon to make sure of unites nature if it allows critical hit and/or multi strike.

well another thing we can do is just come up with a ranking for "maximized" characters (of course i would argue to consider useful unites as a criteria), and a separate discussion about how easy or difficult it is to maximize certain types of characters.

there's a discussion on Gamefaqs about Hazuki, and we tried to come up with reasons nobody cares about her... some arguments didn't necessarily make sense, like being a late recruit--Killey and Cathari are also late recruits but they immediately become party favorites--i realized it's really hard to earn the SP to train all of the important skills to make someone like Hazuki "good" while characters like Killey and Cathari just need easily-obtainable runes popped into their rune slots to shine--for them, the skills are almost irrelevant, but Hazuki is completely dependent on trained skills to be respectable.

So in terms of how easy it is to optimize a character (not necessarily train/max every skill but set them up so they are capitalizing on their strengths), the characters dependent on multiple hits definitely suffer because SP is the hardest thing to obtain in the game.
1-hit wonders like Cathari, Georg, and Killey just need to unlock their rune slots and fill them with the passive runes, which are all really easy to obtain in this game. The "boring" 2-3 rune slot characters who hit hard but can also multi-strike also fall in this category, because generally improving the skills doesn't do a whole lot vs the giant damage multipliers the runes provide.
Magicians are also relatively easy to use because they naturally have plenty of MP and you just have to mix and match equipment to boost the elemental affinity of the rune(s) they want to use.