
So I stock up on Sirens and go fight some damn monsters. Mostly Green Dragons outside Tomra.

Some people were still yet to reach level 60 when I started, but shortly people were passing 70, where something magical happens.
What's New: Natural stat growth stops at level 70.
In 2D, everyone -- even the otherwise-static Fusoya -- got stat ups and occasionally stat downs for every level past 70. Edward is particularly famous for this, because he has the best stat growth of all for the last 29 levels, particularly his Speed growth that leaves Edge in the dust. That entire system is thrown out in 3D.
Instead, the stats you get for each level between 71 and 99... well... you can probably guess.
I mean, think about it. What's the most obtuse, unintuitive way it could possibly be done?
That's right!
Stat growth after level 70 is based on what Augments the character has equipped when they level!
Each Augment has a given stat that it increases as long as it's on the character's action list when they level, and the effects stack. No one can unequip Item (I was wrong when I said otherwise before), so when Item gives HP+10 on level up, everyone is guaranteed at least that.
The other four commands are changeable. Fight gives +10 HP and +1 strength... but a bonus to strength isn't all that important to Rydia and Rosa. You might as well take off Fight and replace it with White Magic (MP +5, spirit +1), Black Magic (MP +5, intellect +1), or Summon (MP +5, spirit +1 AND intellect +1... even though Rydia basically never needs spirit growth either. idgi)
It was here that I learned of a goof-up I'd committed previously. PK Love grants +10 HP, +5 MP, and +1 to every stat at level up. And I gave it to Fusoya because I thought it was useless! I might have to use a cheat code or something to reverse that bad decision.
It doesn't help that the Archfiends' augments are some of the best ones apart from PK Love. They give +1 to three stats. But Porom has Curse, and Yang has Whirlwind and Tsunami. All I have left is Inferno, which is +1 strength, stamina, and speed. Sounds pretty good for Cecil! So I give him Inferno and equip it as I keep grinding Green Dragons.
So not only do you have to carefully plan out how to give Augments based on what they allow characters to do, and to determine which augments you can get in the future, you also have to ration Augments based on how character's stats can grow at endgame! Ha ha ha!
Documenting literally any of this stuff ingame would have been helpful.
Thankfully, most of the things that characters would normally get have bonuses that work for them. Cover grants HP and stamina, for instance. Magic boosts MP growth and whatever stat is used to cast it, or in the case of Summon, both mental stats. Steal and Throw boost Speed.
It takes a little finangling, like giving Adrenaline to Rydia so she has something that can boost her Speed, but overall Cecil and Kain and Edge all end up with 99 Strength, Rosa gets 99 Spirit, Cecil and Kain get 99 Stamina, Rydia gets 99 Intellect, and Cecil, Kain, and Edge get 99 Speed.

Anyway. Why dragons? Well... you know how the rare encounter in one nondescript part of the moon is a bunch of Princess Flans, whose rare drop is a Pink Tail you can trade in for awesome gear?
Well, What's New: There are five more tails! They're all from rare encounters! They're all rare drops! There's a reason I got to gain like twenty levels before I ever saw one. Green Tails drop from Green Dragons, Yellow Tails drop from Yellow Dragons, Red Tails drop from Red Dragons, Blue Tails drop from Blue Dragons, and Black Tails drop from... whoops! Armored Fiends. MacGiants, they used to call 'em.

Trade in one of those tails to the Tail Collector for a piece of Onion gear. All of the Onion gear is described as "{equipment} that grows with the user." The stats you get for equipping it are level-based! Whee!
Cecil and Kain can equip all of the Onion gear. Rydia, Rosa, and Edge can equip the Helm, Armor, and Gloves. Nobody else can equip any of it.
Red Tails trade in at the Tail Collector for Onion Swords. Onion swords have an attack power equal to double the user's level, accuracy equal to their level +50, and give level divided by three bonus to Strength. So after level 75, they're better than Ragnarok.
Blue Tails trade for Onion Shields. Shields boost Defense by one-tenth of the user's level, block all status ailments except Berserk, and give level/3 bonus to Stamina. At level 70 they give a bigger boost to Defense than the Crystal Shield, but never give any Magic Defense.
Green Tails, as pictured, trade for Onion Helms. Helms give a bonus to Defense and Evade equal to the user's level divided by ten, and a bonus to Speed equal to their level/3. They never offer the raw defense of the Crystal Helm or Dragon Helm, or any Magic Defense or Magic Evade at all, but that's a big boost to Evade and that Speed bonus sure is nice.
Black Tails trade for Onion Armor. Onion Armor has Defense and Magic Defense equal to the user's level. So it outgrows Crystal Mail at level 25. It gives a level/3 bonus to Intellect.
Yellow Tails trade for Onion Gloves. Gloves grant a boost to evade and magic evade equal to the user's level divided by five, and a bonus to Spirit equal to, yes, level/3. Level 75 is where they start to compete with Protect Rings and Crystal rings in evade and magic evade, but Protect and Crystal (and Dragon Gauntlets and Crystal Gauntlets) also give Defense and Magic Defense, plus miscellaneous other boosts like the Protect Ring's resistance to fire, ice, and lightning.
tl;dr: Onion Gear is largely better than endgame gear at high levels... as a whole set. Individually, each piece demands a character give up something that the Onion gear doesn't replace. The Onion Helm is nice, but not better than a Ribbon. If you want the status protection, you need an Onion Shield, which only two people can even equip.
Further, only the Gloves and Armor give any Magic Defense and Magic Evade, and by the end of the game it's not physical hits you're worried about. It's Dark Sages with -ga magic. It's Blue Dragons with Ice Storm. It's Red Dragons with Atomic Ray. It's Deathmasks with Flare and Holy. It's, y'know. Zeromus with Big Bang.

And if you're going to grind out rare drops for a piece of armor, why not just grind Princess Flans for Adamant? Adamant might give half the stat bonuses of the Onion Gear, but it does all of that with only one equipment slot, adds elemental resists, and adds status resist. And has Defense and Magic Defense better than the Onion Armor at level 99. And grants more Evade and Magic Evade than the Onion Gloves.
what
then
was the point
I know it's hard to beat the intentionally super-rare and super-overpowered armor from the core game, but sheesh, balance it out somehow. Maybe make the Onion gear a easier to get than the exact same drop chance from Siren-summoned monsters?

Long story short I went through like 300 Sirens and got everyone to level 99 and all I've got to show for it are two lousy Onion Helms. I probably should have switched from Green Dragons to Princess Flans sooner.