I am by no means an authority on FF but I'm currently playing XII TZA with the struggle for freedom difficulty mod and I can only recommend it.
I was going to do just this, but the modder said if you wanna start now, hold out because the next big update should be done by the end of the month. I'm sitting on the edge of my hands because I typically play FF12 once every year.
Penelo is definitely a tagalong, but Vaan is there to serve as a mirror to how Ashe should NOT act and feel towards the Empire. Her hatred, rage, and thirst for vegeance are meaningless, and will do nothing but make her feel even more hollow. The game flat out tells you this during a cutscene in Jahara, after asking the Village Chief about the Nethicite. It's also why Vaan doesn't see the ghost of Rasler a 2nd time, he left his quest for vengeance behind, leaving the Occuria no strong emotions to exploit and play puppetmaster with.
It was the same thing with Balthier, only time he ever saw the Occuria was the flash of Venat when he saw Cid in the Draklor Laboratory.
Though Balthier and Ashe were the main characters it still follows a semi-ensemble cast much like FF6, the only real big emotional reveal the game offers you towards the end is between Gabranth and Basch in Pharos, which really hints towards major story changes late in development because of SEs suits, unfortunately.
It's safe to say I consider 12 the series' opus regardless of the game's development strife, as it was a combination of exploration, difficulty (if you pushed the hunts ASAP, and hit all the endgame content), without delving into stupidity like Emerald Weapon grinding and watching Knights of the Round for an hour, had enjoyable cutscenes, and a unique setting. After that it would be 6 for the 2nd half of the game, then 1 for freedom, followed by 9 and 7. I'm not including Tactics because I feel it belongs in a different set of games.
All that said, while I wait for Struggle for Freedom's update, I'm playing Summoner 2. Shame it hasn't gotten a Steam release even though theassively inferior Summoner 1 has. It ditched the boring RTwP combat for a straight up ARPG that lets you pause the game while selecting targets for spells and the like as a better alternative.
The characters are unique enough, with Maia, the protagonist being a hybrd melee / caster / healer who can shapeshift into various creatures with different strengths and weaknesses, her general Taurgis, the game's brute, and Sangaril, a stealthy assassin, amongst others like a Hand-to-Hand Monk with superior healing capabilities, a Soul-Sucking Giant, stereotypical bearded Wizard, and a robot with a gun-arm.
The gameplay varies itself enough that it's never really boring, and forces you to use every party member at some point, splitting them up in groups of 2 or 3, and allows for gameplay changes such as using Sangaril's stealth function to sneak behind enemies, avoid detection, and go for a OHKO backstab. Or use Taurgis' slow-footed nature to fight equally lumbering beasts in 1v1 or 1v2 fashion. Neru gets to fight up close and personal, and use different stances for offense, and defense proving quite useful against armored enemies resistant to slash and pierce, while being the game's premier healer.
Content-wise, the game offers oodles of sidequests, with little to no guidance, and may even require you to jot down little notes of points of interest the game throws at you in assorted areas. Unlike most games with a massive town / questhub that I absolutely despise, the game does a good job of keeping the content condensed within, and doesn't have to resort to a huge town with a loading screen every 20 seconds, or backtracking to the same spot 7 times. Most backtracking can be completed with a single load screen, if any.
It also offers some mild C&C in deciding how Queen Maia should handle petitions from her vassals, and nobles of nearby nations. Though most of them do have optimal rewards (like any other game), getting to choose whether Maia is a fair Queen, or rules with a bit of an Iron Hand, such as denying a Princess access to a royal tomb to bury her Father's remains for past transgressions is kinda fun.