Yes. The only use for Samurai Raegar is against pure tanker team, which do little to no damage against your team unless you tried to breakthough faye's return damage barrier. And that only when the fear debuff kick in. Which is not that often anyway. Unless the fear kick in, he'll deal little to no damage to the enemy since after taking over middle tile, unless there is an enemy right next to them, the guardians will simply defend. Otherwise, the guardian will only take damage from bleeding once.
Against all other teams, especially with archers in it, or mystic+guardian team (which doesn't revolve around mid tile takeover, usually include CK Aden, and clustered on the corner, which reduce bleeding damage potential), he'll be among the first to die. Guess what team most used on Everglades server? Yes. exactly those two kind of team. So I suppose you are right when you say it's an Everglades bias.
And since his celestial form has melee range normal attack, he'll have to move forward or wait someone to come within his range to be able to use his on-attack effect.
Believe me I tried. I got Raegar on first day of his event (along with emillia), build a samurai, and tested him for a week long.
The result? I benched him, then ended up using him as fodder. Why? Because he's just that disappointing (and that I have another Raegar I can train if I feel like it).
Yes there is maybe a build like combo-ing with Kiera Warlock to force move the enemy. But unfortunately I don't have Kiera Warlock (yet). But it'll be only useful if we cast the skills back to back. Also, correct me if I'm wrong, knockbacks don't trigger bleeding effect, so Rune magus and grand ranger cybella is out of question.
IMO, Raegar Magebane is more useful than Samurai in term of arena utility. He can be useful on archer team since his aura is attack trigger type, and he becomes ranged unit once entering celestial form. On Mystic team, he can be a little useful to by-pass opponent mystic skill damage defense (not that useful against other classes because either they have low MAG already, or they are too tanky to be killed in a single skill). Against mystic team, he can be useful to mitigate damage from nukes.
About skill cooldown, i forgot to mention that it's just for some of them. Some elves with 3 turns cd is okay. But the ones with 4 turns cd suffer from only be able to to cast their celestial form once per arena battle, unless you are up against a very tanky team and you (or your opponent) hasn't ended up winning the battle from point accumulation.
Take Emillia (both classes) and Altima Paladin.
Altima Paladin usually can only cast her skill ONCE because her celestial form lasts for 3 of her turn after cast. Most arena battle doesn't last that long. Plus, her return damage is reduced by enemy's MAG, it deals pitiful damage to mystics. Her only absorbing 30% damage doesn't really protect squishier units at all from mystic's nukes. And her melee type celestial form make her on-attack effect rarely useful on arena. Even on the off chance you cast her skill on the right time, it doesn't really protect your squad that much and the return damage is rarely a satisfaction.
Even on PVE, the paladin is outmatched by Faye and Darrion, because the two can cast their party protection more frequent in long term. But I guess this is deliberate design. Still, her skill will be more useful if she absorbs more damage, or return more than 100% damage taken by her, or if the celestial form lasts quicker than it is now. Yes, the celestial form make her tanky, but only if there is no hindrance for her to hit the enemy.
HD Altima at least has better prospect, since we may actually build her ala the now popular sdd Leon. Plus, she doesn't have to wait that long in order to re-cast her skill. Albeit her celestial form is quite suicidal on her own part, at least it does a great job in protecting allies.
Emillia Inquisitor has to rely on external healing like altima paladin's celestial form, healing per turn of Archbishops, and healing on getting hit from various guardians and healer classes, and lifesteal aura heroes. Why? Because most of the time she can only use her healing once per arena fight. This is a good design in order to not make her OP, yes, I must admit. Just that outside of arena, her healing capability plummet if compared to the likes of Luthor and Matilda Spirit Walker (which has similar build). She can be very very strong if we build her talent, same case with Leon and all other characters for that matter. But building talent isn't something a non-whale can do real fast. Also that Matilda Spirit Walker has more utility than her as similar kind of 'battle priest'.
TLDR, it's not that I'm against the current system. I'm just irked with how I need to wait for full 4 turns to cast paladin's half-assed party protection skill when others like Faye and Darrion (whose skill does better job) only have to wait 2-3 turns. And the fact that for the return damage to deal substantial amount, it only means that most member(s) of your squad has already been obliterated or near death. Her only saving grace for me is her aura, and if she can actually hit people during celestial form.
Same case with Emillia Archbishop. I'm still keeping her for collection purpose only.
Also about how niche Raegar is..
And that the only elf with 4 turn cd celestial form that I find pretty good so far is only Grand Ranger Tess'.