“I don’t have a 5* Astral Elf (or Tametomo et al.) and may never get one” isn’t … that niche.
I mean, sure, a Toon sniper is going to be “75%” 
immune to blind or having its Special stopped, but Gladius takes that to actually 100% and, of course, ignores dodge. (Or Wu-Kong-style-buff “dice” miss chance, if it matters…)
I mean, amongst bigger spenders or players luckier with summons, sure, probably have several “this Special skill never misses,” and of course the Scorpion Queen is superior for dealing with dodgers if you can get her.
(And I’m not talking about Gladius’ “tags a foe with a stack if they dodge” which is hardly even tertiary.)
But “I don’t have even any of the latest flavor of premium hero” isn’t, like, THAT narrow of a niche, and someone like Gladius at least gives proles an entry-level version.
–
As for Casmir, here, I kinda wonder that a Phenexa-Casmir-Ukkonen combo wouldn’t be… reasonably decent (and also attainable for at least some modest to moderate budgets, given the recent SE Phenexa and the current cUkkonen in Kalevala).