If you intend to make multiple cores, you’re gonna want multiple high merged legendaries. Otherwise, making multiple Arena teams is pointless, because the only real reason to change is to benefit from that season’s blessing scoring
So let’s take a look at your legendaries
For Water: I see merged Dimitri and Chrom. That’s good, they’re both great. Dimitri offers greater scoring but Chrom has a high scoring movement assist, which is incredibly rare and valuable in Arena, so it comes down to preference
For Wind: I see merged Lucina and unmerged Gunnthrá, Eliwood, and Corrin. Corrin offers the best mix of usefulness and scoring but being unmerged does her no favors and you won’t be getting more merges anytime soon. Eliwood is… pretty bad for Arena, frankly; I’d skip him. Gunnthrá is an interesting choice with her new Chilling Seal II, but she too, needs merges (she also wants a G Duel Cavalry for scoring, and that doesn’t exist yet). And Lucina got yeeted to next year so she won’t be getting merged anytime soon
For Earth: You have a merged Claude. Use him and merge him more if possible. He is head and shoulders above the other Earth legendaries
Fire: I see you have Marth, Roy, Hector, Celica, and Edelgard. Unfortunately Marth and Roy suck in Arena, and Hector is not much better, so I’d focus on either Edelgard or Celica
Merging these units is extremely expensive, but if you want optimal scoring and are building multiple teams, you gotta invest in them
If you’re not gonna do this, just pick three units that cover each other well and roll with them whatever season it is. Blessings are useless (aside from the increased SP) without a Legendary unit’s help, so making multiple rotating teams just for Arena without legendaries is a waste of resources.