Share a or Eirika?

I’m planning on making an arena core, but IDK wether I should include Eirika or Sharens (+Speed -Hp Eirika btw)

I love Sharena in general, but she doesn’t have IVs or merges, whilst Eirika does, and I am conflicted on which to use, I could probably use both but they both have mediocre/bad offensive potential (at least I think)

I am willing to invest whatever is needed into either, and I am certainly willing to S summoner support Sharena. So all in all who would be “better”