I have been lucky lately and got double costume elkanen, guan yu, diaochan and used SE to take ludwig. Ludwig and Guan Yu are both paladins and I only have enough emblems to take one to 15. I also only have enough aethers to take either Elkanen or guan yu to 85. I also have enough aethers for either diaochan or ludwig. I would have to strip emblems to take Elkanen to max from non costume ariel. I still use her sometimes, but I have diaochan and rhys as other legendary healers.
I think the correct choice is LB/emblem guan yu and diaochan and leave elkanen and ludwid at 80, but elkanen can be over a 1000 power maxed and adding survivability to ludwig would be nice, but he is only playing offense.