Roster strength has no bearing on bracket type. You need to look at the performance record of players in the bracket. If you are not familiar with the big PvE grinders, then post the names of the top 10 here and see if anyone else can recognize them. Alliance affiliations can also be a useful proxy, as the top PvE alliances typically have no slackers.
Slice 3 with Shawty45 on the top of the leaderboards has 407 players. The entire top 10 has 7k+ points right now. Assuming this is a vet bracket, but I don’t really see any players I recognize.