Summoners useless in 24mans?

[Vmage]

so yeah, roughly 18 debuffs at any one time if there's 1 SMN per group.

don't forget thunder

it may not affect fester, but it's a lot better dps than ruin, same goes for shadowflare which may or may not be taking up a debuff slot with slow (although this is probably the best debuff there is so it should absolutely have priority)

I don't attribute ruin II to summoners as the tank is probably (should be) flashing anyways

but yeah, if you wanted to count defensive debuffs that may or may not be important depending on the fight, we could look at virus taking 2 slots, eye for an eye proc taking another