I have mostly played melee types and, at times, felt somewhat superfluous when a caster brings out the big dawgs from the astral kennel. I recently tried my hands on a caster shaman that relies on summons to provide cover for his archery, and I agree that before the nerf, summons were too powerful.
But the nerf hammer hit a bit too hard. For casters, as many have pointed out, summons are essential to handle PvE content. It is simply not feasible to play a caster solo without them, unless you are a warlock/spellsword or have some other way to combine high defence and a pool of offensive spells/abilities that do not run dry. Divine casters (aside from druids) usually have none of those.
Zen caster archers will have their niche, but a dip in monk or vigilante for AC is now mandatory when your summons can no longer be relied on to provide cover.Teaming up with a martial character or nabbing a pair of henchmen is a way to mitigate the problem, naturally, but they may be in short supply or unavailable when you need them.
In conclusion, I don't mind at all that summons are nerfed, but I think this went a little too far. And summons should absolutely be brought in line with each other, so that one feat (DC) does not outshine every other epic summon. A three feat investment in spell focuses should be rewarded.