Off the top of my head, Characters with similar styles/lore power/artes that would be pretty evenly matched:
Suzu and Jay
Cress and Flynn (but Flynn has the magic) and Chloe (3-way match)
Arche and Kongwai (Grune without her plot powers)
Chester and Chelsea (possibly)
Woodrow and Hisui (though Hisui has the really great healing abilities)
Leon and Judas.........
Mary and Forest (TotT)
Farah and Regal
Kyle and Richard
Harold and Jade
Reala and Elize
Loni and Eugene?
Genis and Hilda/Will
Colette and Lailah
Veigue and Ruca, ish one blessed by a deity thing, other reincarnation, both heavy, somewhat slow hitters with one significant element, maybe not the best matchup though, I feel like a Ruca matchup is on the tip of my tongue, maybe Ruca/Alvin, but Alvin has the gun thing going on and not as much plot power
Norma and Beryl possibly, even though Beryl can be a bit more offensively capable
Tear and Rowen?
Illia and Mikleo mixed together unequally kind of reminds me of Hubert but that's just gameplay-wise, lore-wise I have no idea
Hermana and Sophie (though i feel with everything there is to Sophie it leans more towards her)
Cheria and Lailah are similar battle-wise, but lore-wise Lailah and Colette are a better match
Leia and Mikleo?
Ludger and Rose/Karol/Illia? not really lol
Muzet and Dezel/Zaveid
In general Muzet/Milla/Reid/Sophie/possibly Spoiler!Asbel should be on par with Armatized Shepherds probably, or somewhere within that realm of power
Pascal/Max/Ricardo/Edna all launch things???
Going over things, a lot of character share some similar styles or artes, but overall as a package with their lore it's hard to compare for me. There's enough to make MOST characters pretty unique and just different enough not to be a good complete match. There are several classes a lot fall into though, I mean, in general we have a lot of Magic Knights (Kyle, Kratos/Zelos, etc.), a lot of mages that have some physical attacks, there's at least one character that uses Cress's brand of artes in each way with a unique spin at times, in most games (Cress, Lloyd, Milhaust(ish), Chloe, Guy, Spada, Flynn, Richard(ish)), speedy characters (Repede, QQ, Spada, Kunzite, etc.), etc. etc. The ones I left are the ones i felt matched both battle capabilities and lore capabilities.
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