Neith is a stalling tactic - she doesn’t hit that hard, but she delays specials to buy your defence a turn or two and she blinds incase enemies still get their special off fast.
Telluria is also a stalling tactic with mana regeneration reduction on top of minions and HoT.
Put them together and they’d be annoying to face… But neither hits hard, so the rest of your team needs to be nasty to attackers - and it looks pretty decent for that.
Justice hits a bit harder than Neith and keeps the blind… She’s slow, but with a delaying tank like Telluria and with her own considerable beef that could work on defence - but the mana speed could make her more annoying to use on attacks.
Leo is decent, nothing wow but nothing to laugh about either.
There are drawbacks to all of them, however.
Neither Neith nor Justice is the best blinding holy 5* - Drake has more impact than either.
But Leo will really fade into the background if/when you get better snipers, eg: Joon (esp. with costume) or Poseidon.
For a bench with no holy 5* mana control or blind, Neith gives you both - if you had Guin or Drake done, it may feel like a waste of darts, but she can be a pain to face in the right teams, regardless of how much people rag on her on here.