Yeah but...with no buffs at all, a unit of morrsarr does more damage on the charge (by a lot), they aren't monsters, they have 2 more wounds, they move faster, and deal mortal wounds. Alloplexes feels like a tax in the Corps.
Given, supreme Lord of tides does help this, but spears only loses a little bit of ground on the bite per command point spent and the buffed fanged maws and lashing tails of the guard are enough to outperform the buffed hooks and fins of the alloplexes. Adding attacks to these outweighs the potential benefit of the increased attacks on the bites.
If you're worried you can't charge the enemy, then yes, alloplexes will outperform on damage but you're probably in a bad way. Fuethan actually makes eels worse so it's a good one to pick for eel-badness.
I think alloplexes feel like they're "missing" something. That's why I want a rend on their shooting.
As a side note, I'm currently painting 3 of them. Don't get me wrong, I love these guys. But I can't defend that they are a good competitive choice. I love the models and I think they're fun and fully support anyone who wants to field them. If I ever played against alloplexes when someone had a box of eels they could field, I would buy them a beer.