I'm not sure about that. With already 4 lavinia in the deck, plus recall and time walk, you already have 6 blue cards. If you put 4 fow and 4 misstep (which is kinda the basic fow package) you have already 14, then you can put somethings like phantasmal, fluster, deep analysis, treasure cruise. I mean, you don't get to that point where you have to stick awkward blue cards (as the bug version also don't).
One weird and which makes thalia bad IMO is that with thalia, free spells cast 1. I'd rather pay 1 for a spell that would be free, than not be able to play it at all. There's that other clause that's still pretty good (non-creature with cmc>land can't be cast), but you lose half of the Lavinia's power. And I dare to say, you lose the best part of her. They are both hatebears, but instead of stacking they are bad together.
Now I think we have kinda 2 main ways to go, which are counter or thalia. Unless we get to a third way, Lavinia will probably be played with fow.
BTW, Just played against PO with Lavinia+karakas. That's definitely something to watch out for, Lavinia is awesome against PO but for combo decks it also protects them against fow/misstep, and in our case, rootwalue and hollow one too. It's not lights out, but its a pretty good card against survival.
Considering they have both karakas and lavinia (which are both strong against the leovold survival), I'll stop bringing in nature's claim and instead board in assassin's trophy against PO.