No one could tank Naila on ultimate in a lengthy battle without any healing. Rather, the way to do it was to have Ortylia use her regeneration skill, then switch characters to someone with a strong damage skill that you can spam several times for massive damage. You're invulnerable while using a skill, so it doesn't particularly matter if the character was fragile. If you run out of SP before Naila dies, then switch back to Ortylia, use her regeneration skill again, then switch to your other character to spam damage. Claire was pretty useless because she can't spam damage.

Claire as support would use skills to increase your own damage from skills. That's why she seemed nice as a support character. It wasn't because of the damage that she did herself.

It's also worth mentioning that Naila on ultimate was by far the hardest non-raid event that has happened since launch. I'm not really expecting that difficulty to be repeated, though I hope they do.

For arena, you want to have several girls powered up and ready to go so that you can send out there whoever you need. That way, you can send out send out a good counter to whatever your opponent has. The girls I personally use in arena are Charlotte, Perille, Eremia, Leina, and Seleia. Seleia is mainly to kill an enemy Ortylia, as 2876 crit makes it very hard for an enemy Ortylia to land a crit and have tempting chaos take effect. In tower of trials, I'll also use Ortylia for the regeneration, mostly to use the skill at the start of a battle, then switch to a different girl.

The other girls that I have powered up are Grace, Elnora, Naladia, Zephyr, Chharodi, and Summer Naladia. I don't use them much, though. Summer Naladia was free from an event, while the rest used to be part of my main team and were replaced as I got stronger options.

Charlotte and Perille are probably the most overpowered girls in the game. You had to get Perille from an event, but it sounds like you did, unless you're using a low star version, which is bad.

For wind girls, the big three are Leina, Khalis, and Eniel. Khalis isn't very good at arena, Leina isn't very good at raiding, and you have to whale to get Eniel, so you can choose your poison there. Khalis seems to be the most common, but I use Leina because she's better at arena and tower of trials.

For earth girls, there aren't any notably strong ones, at least excluding ones that you had to whale to get--and I'm not sure if there are any of those, either. Eremia is probably the strongest at arena. Chharodi may be the strongest at raiding. Claire is only for support, and Ortylia makes her redundant.