Search yielded no results, so let's talk 5* Fac.

Imo almost any character who's 5* is useable in arena. I think you're missing out on maybe 10% health and a few percentage of damage points you get in the jump between 5 and 7*. Gear and mods are much more important to a character's viability. The only issue there is that people will see a 5* character and target you more.