I am really enjoying this mod so far! I don't know what direction you want to take this build, but this is what I think:

As someone who never really cared for Warrior classes, I would love it if the Tempest could sort of fill that role - albeit in a completely different way. I don't know how much manipulation you can do with the game's mechanics, so I apologize if I offer an idea that's impossible X-D

I love the idea of applying useful CC that isn't resisted by armor/magic-armor - particularly on statuses that players don't have much access to - like fear (which you did) and entanglement. If you can't make a status ignore the amor check, instead you could just have attacks drop fields that do this - such as oil for slow and ice for knockdown. I think if you emphasised this a bit early on, you could have the Tempest basically be a mobile CC machine like a Dervish - using scoundrel+spear range to cripple enemies and then swinging in with piercing damage to finish people off no matter their native resistence.

Right now all of the early skills apply bleed - and I don't really see the need for that considering you have to wait for your other characters to drop their armor before using these abilities.

Sweeping Slash - damage and drop an oil field (or apply entangle).

Piercing Thrust - could this apply the scoundrel's Sever Tendons effect? :-D

Poisoned Strikes - since we already have Envenom Weapon, how about a high cost (3ap? I don't know balancing X-D ) jab that apply's Acid (I think if it just hits a single target you wouldn't need to add a source cost to balance it). Or maybe it gives you a damage debuff for a turn to two since your weapon has melted :-p

Necrotic Strike - I just love this :-p

I think it was smart not giving the Tempest a true movement skill until the Adept level. Their reach is already quite good, and since it requires Warfare and Scoundrel you already have access to their movement if needed.

It could also be interesting if you were able to allow spear's to use the elemental arrow items - since they use a similar tip :-p Again, this may require a damage debuff (or if possible it could be a skill with an apropriate cooldown)

And honestly, I kind of like the current skill icons X-D

Anyways, I don't know if you already have too many of your own ideas and don't really need any more, or if you like it when people throw theory-crafting at you :-p This is just my way of sharing my appreciation for the work you're doing! Thanks!