Sylvan never felt that op to me, at least not to a Magnet warrior deck. SSA is quite strong indeed, but most players do not play it correctly, protecting Water monster by banishing it leave an open field. They also need 2 monsters to summon a that freaking whale, so it'd be a shame if something were to happen to one of them when you summon that second monster (gotta love Triamid pulse)
SSA can be handled by common card such as Floodgate or Cosmic Cyclone.
Slyvan is good but not OP, can get bricked real good. The rather difficult one to handle is actually Golden Fish but that too can be handled by Floodgate.
Overall it is not unhealthy like during CA era where everything in the deck can be searched and recycled. Countering common legend deck can be expensive though.
To be tier 0 a deck must need a very specific counter deck or they can only be countered by their own deck.
Sylvan can be countered if the first set card is destroyed or returned to the hand, something that SSA, Golden Flying Fish, and any other deck with Tribute to the Doomed can do.
Book of Sun can be used for instat flip but it is not reliable.
Saying "x card/deck is countered by y card" is pointless considering you might never get the card in time. DL is very RNG heavy. This is why imo the 5 consecutive wins condition for KOG is absolutely 🔥ed.
That is why I said earlier that countering common legend deck can be expensive.
And yes, I still hate it that even I can't gather cards that counter common decks in legend. That is why I never bothered for laddering and just aim for reward ticket.