Definitely don't see Revya as non-rankable.
Those stat boosts aren't really random - I can check to be sure more specifically, but I've seen them listed as set boosts, and have also seen them like such myself during the game. They're set boosts, like +18 INT or whatever. So the randomness argument doesn't work.
The game is basically Ogre Battle, though more polished. Same thing with squads, just with the room thing. While there is a synergy with other units in the room, it's perfectly normal in-game to see a single unit in a single, normal room (Layna in the Demon Path, IIRC, as well as some random monsters throughout the game).
Now, the HOME room can be changed as needed, and isn't random - you could argue Revya has access to any room possible, which means she's far better than a Low Godlike - crazy evasion room mauls those without multiple-hit attacks, stat boosting rooms when solo, etc.
As for summoning...it's more akin to Marona than anything, I'd say? Unless you allow summoning of generics, since I would assume most people...wouldn't allow summoning of other PCs.
Really, really don't see Revya as unrankable. Still isn't exceedingly fast, relatively status-vulnerable, doesn't get initiative that I remember (I've surely seen Danette go first - I might be wrong on this, but unlikely), is purely physical. I honestly don't think there's anything unrankable about Revya that we haven't done already - the stats thing is more like if a character started with an item that boosted stats on level up (like TotA capacity cores), and was the only member of the cast to get one and had a claim to it...would they be unrakable? I mean, what about Grandia stats from weapon/magic levels, or runes/mediums in the WA series, or SMRPG ability to choose stat bonuses on level gain? Should we not rank Chuck because he has a starting medium, or not rank Mario because he can theoretically modulate his stat growth (or Serph, for that matter - ignoring the fact that, in the SMRPG example, they eventually even out)? It's one of the advantages of Revya in-game that she can get more statistical bonuses via her mechanic. Really, really don't agree with the unrankability argument.