What Tera or item is Zacian gonna do to stop Tina and Moltres from Roaring it out? Quagsire does lose if you don't tera but when fighting vs Tblaze Zacian its either dying or committing Tera, so why are people hesitant on committing their own Tera? And If I saw Wcharge + Tblaze thats some mega hating and I would be very concerned for viability.Okay, a few things
1. Trailblaze Zacian is not losing to the defensive counterplay you listed given the right item, coverage or Tera, since , Quagsire loses to any variant, Terapagos loses to standard Trailblaze and especially hard to Tera Ghost variants, Clefable and Dondozo lose to Tera Fairy boosting item, Moltres and Tina both lose to Lum Berry variants, and are forced to Tera before Zacian is (Moltres is a guessing game of is it Wild Charge which by itself is quite losing).
120 Atk with 90 BP moves will have a very hard time wallbreaking when you look at the rest of the tier, definitely not very crazy after initial boost is no more. Also feels far worse to commit tera on because its no longer consistently blowing up whats infront of it. Sub/Tblaze get the same tratement, phased out or unawared on.2. Saying Zacian is a one time sweeper is just wrong, yeah, it's considerably easier to handle after inteprid but it can very much come in early, wallbreak for itself, come in later in the game and clean up, especially true for Substitute or Trailblaze variants.
Not quite, boohoo my Quagsire or Solgaleo took a little under 50, reveals itself instantly and honestly makes you relieved since its much easier to handle and theres a lot more room for error.3. All of this is without mentioning the entire ramifications of Choice Band variants, who are by themselves amazing and completely change how you handle Zacian