As a Gishki SSA player I can confirm Cosmic Cyclone will happily me royally. If they use Mystic Depths, banish the Umi as SSA can't pull Umi back on to the field. Chances are there isn't another Umi in the deck, rendering SSA useless. Divine Wrath/ Ulti Prov is also a scary counter if it's saved for the whale.
I've told you Thiccer Insect Queen deck is the way to go. But if you really want an absolute counter, you may want this card, this counter MASKED HERO, SSA, and Geargia from using Ties of Brethren. But the downside is it become useless when you face Sylvan
Anti-Magic Arrows will stop SSA from working during battle phase. You can also use Spiritualism to return Umi/Legendary Ocean to hand. Both requires you to OTK the SSA user though. Make sure you have a combo to achieve that.
As an SSA player, I can confirm that AMA and cosmic cyclone is a nuisance. At the same time we have to get the right combo right away, which is why we run balance or restart. I have also lost matches, especially to sylvans, even when I get a good start because they force me to banish and then they flood and OTK. Its a good deck but definitely beatable.
As an SSA player, CA is a good counter but I use SRH to have a chance (Hymn of Light can't protect against SRH AND SSA). Sylvan is a 50/50. Masked heroes too. With a LVL 5 + ALO + SSA and Econ, SSA deck is unbeatable by 90% of the meta, except CA.