[Agema]

Indeed.

You should view FFs as major battle mages. This is because Angakoks are limited to the capital so might not be available in large numbers, and 1D1W Tungaliks are simply pretty weak mages unless you're facing undead. You'll probably want to free up vital Angakok manpower by switching a lot of your water and earth summons, crafting and rituals to the FFs.

25% of your FFs will be W3S1; W3 obviously grants access to plenty of water's heavier hitting stuff. With gems and water's cheap and easy Con-4 and Con-6 boosters you can readily access lots of the really powerful W4 & W5 stuff and lay it on thick, with no Angakok needing to be in sight.

As you point out, your W2S1F1 can access acid spells, which are pretty nasty. It's a great way to catch out opponents who have prepared against lots of cold damage, and there's no such thing as acid resistance. Get one onto land, should be able (I've not tested) to cast Manifest Vitriol? Ethereal, acid-breathing, 25ish HP lions. They can be absolutely devastating.

The W2S2 give you major astral support: Antimagic is quite a defensive boon, especially if you've brought plenty of undead along, or if you're facing Rlyeh. Other obvious options are Paralyze, Stellar Cascades (which fits in with fatiguing tactics), and why not horror mark the odd SC/thug as well?

The W2S1E1 will be useful on the battlefield, although you won't normally be leaning on them. Everything Baalz said in the first edit about Angakoks and E magic applies here also. Where your Earth-capable FFs most come into their own (in my view, anyway) is crafting. The E/S crystal range (Coins, Shields, Matrices, etc.) are extremely powerful when used properly, and these guys will get you there.