Summoner is better than black mage at the moment in the majority of savage, so I'm not sure why you would be hearing that it is doing 'poorer', since black mage is its only competition for the caster spot. Maybe they are comparing it to melee? If so, that's pretty irrelevant in an 8 man group.

It's a very strong job, a little lacking in utility perhaps (unless healers die for some reason), but there isn't a serious raid group that wouldn't be happy to have one.