Summoner support + Elincia build advice

Hey guys!

I just can't decide what to do about my summoner support, so I was hoping for some advice on the matter from this great community.

My current support is Brave Ike (+Atk -Spd). He has vantage + all his other default skills. However, yesterday I managed to pull a +Atk -Res Elincia, and she is absolutely incredible in player phase. She is so strong that I started to think about changing my support to make her a complete goddess. I mean, they are both good options for summoner support, but I just can't decide.

At the moment Brave Ike's stats stand so high that he is really really hard to kill. If I remove the support he will be a little less powerful and less bulky. Maybe giving him distant def seal can somewhat patch that loss.

On the other hand, supporting Elincia would increase her stats to 51 atk with atk +1 seal, and 36 spd. Res and def would get to 26, and hp to 40. With that bulk, it wouldn't be a bad idea to give her L&D3, which would make her freaking insane with 40/56/41/21/21 without any kind of buff.

I just don't know what to do hahaha. My arena team is Brave Ike(he is kind of a staple due to his high BST), Valter+2 (with L&D3 and desperation), Elincia and Brave Lyn. I plan on changing Lyn for the Black Knight when I get him, with the objective of finally staying in tier 20. I haven't been able to do so, and maybe that team won't be enough, but it will get closer to the goal.

So, if you were me, what would you do? Support Brave Ike or Elincia? Also, how would you build her?

Thanks in advance and good luck with your summoning!