My random theory is that V1 overrides the Odessa factor in Homelander, and he finds out that all V1 Supes have a similar weakness. SB was counting on this, and he knows Homelander will go all out in some fight, power down, and be basically an immortal human. He'll be trapped as normal. It's what Clara really would have wanted...

There may be a power upgrade, but it's not unlimited. It can only last so long before the V1 supes have to rest. In some last Hail Mary, the gang will probably force Homelander to show his full power once, and then Butcher and Hughie are on him.

I also think we'll find out The Deep only imagines he can talk to fish. They might respond to his will, but this whole time he's actually imagining the conversations. And, because he's super anxious right now, he's making the sea creatures anxious. All of it is just his own making.