Mimes have some of the best stat growth of any generic, but yes they're not really worth the investment (deleveling and releveling is just overkill for this game's limited difficulty), if you pair them with Bards and Dancers, you can commit a lot of shenanigans.
On that note Bards/Dancers are slow, and their abilities are nearly entirely Stat agnostic, and are simply % based, but they can do some pretty cool shit, but there's a lot of other classes that would work as well and require less effort. I say that after just Mastering bard on Ramza, initially for move+3 but now I'm not sure if I'm gonna use it as my secondary or Iaido.
Regular Squire has pretty bad stats, but you get JP Boost, and in my opinion more importantly Focus, which you can just spam over and over for JP and +1 to Attack, e.g. my Generic Dragoon just hit a mob with brawler for 999 in Act 2, after JP grinding for a few minutes. Focus is in my opinion the real most OP'd ability in the game, since unlike other passive boost/jp ups you can get it in the first battle or two, and early on you'll have a lot of units that are just waiting for enemies to pull up for 1-2 turns and instead just them having their dick out waiting, you're passively skilling and beefing your PA
Geo, I pretty much never used in PS1 but they get solid PA and HP growth, and Attack boost, I plan on adding the Attack Boost to Agrias and my Chemist/Knight, their spells are MA which they don't have good growth in
Thief, Oracle/Mystic, Mediator/Orator - Are utility classes that have very valuable functionality, but in very limited circumstances, and aren't significant outside of that
Time Mage and Priest, aren't worth it in my opinion, unless you're adding them to your math skill. At 3k GP I'm not even sure Teleport is worth it, at least in the early game anymore.
Black Mage is a solid glass cannon with a female, and high faith (Magic Boost which is useful to Calculators post nerf). Summoner is supposed to be ok, but I'm not convinced given they're slow cast
Goons are Tanky, and have good attack but they're slow (if you want to skill them up, don't bother with any of the lower tier jumps just grab the highest Vert and Horiz), Ignore Height is pretty good for certain maps, you can use their jump as a secondary on Ninja, and equip flails to do good damage.
Samurai has poor MA stat growth, so is often ignored outside of Blade Grasp which is broken, but Ramza's Squire get's good MA growth so it's not bad to subclass for him.
Monks, Knights, and Chemists are superb especially since you get them so early
of the generics, I'd say the most unessential is Archer, they do have concentrate but you can get better Support Abilities as early, they're just a gate keeper
My opinion the second best job is Ninjas, yes their stat growth outside PA and Speed is bad, and their throw skill is middling, but they have innate Dual Wield, Stacked with Brawler they are capable of the most single target damage in the game, or just use sword, they are still going to probably kill most things with one double attack. They can be built to make it across the map and kill a unit on the first turn, they're an assassin for all intents and purposes (but better because you can't be immune to physical), and thus broken.
The best skill, not just generic skill, but best skill in the game (but only if used as secondary to a high MA job) is Calculator. They supposedly nerfed it in Tactician, but my understanding is not enough for it to matter, which is an indication of how broken, and which is why I avoided it, I tried playing WOTL on my phone years ago, and went hard in Mini/maxing and stopped progression at the Roof top fight. It's not that it was a a difficult fight, I could end the battle in one turn...I was trying to steal the Accessories that the Assassin's had, I don't think they were even one of a kind, I just wanted them early. Then I think I was messing around with deleveling Stat growth or something, and kinda just got bored of the grinding for the sake of grinding, for what was totally unnecessary overkill in the first place
