I was a summoner for all of the last raid tier. Believe me when I say I know what their old Aoe capabilities were. The problem? Every Aoe that summoner has except for one has been gutted or nerfed. While Black Mage, Ninja, Samurai can easily surpass Summoner in Aoe with dragoons and monks being able to do enough while still having high single target damage. Samurai wins the aoe contest with their 800 potency aoe, but Samurai wins dps period. Ninja's are the most notable in my opinion with Ten Chi Jin being able to be a stronger deathflare with no damage fall off(making a 500 potency katon). Oh and speaking of which, Katon which is now buffed from Ninja's losing poison and gaining passive damage increase to everything (Not Just physical Damage), Kassastu, and being able to deathblossom. So let's take a look. ten Chi Jin 500 potency katon and hell frog medium 400 potency vs Deathflare 400 potency with fall off. Two Katons at 250 potency with one guaranteed to crit on all targets with kassastu and are 50 base potency higher then painflare and instead of bane, which does 64 potency for the second enemy, and 48 for the third, Ninja can death blossom them all for 110 potency each. Not to mention that ninjas can get 4 katons/dotons per minute and can very quickly build enough gauge for hell frog which is just a massive dps gain. Oh and Ninja's can buff the entire group's damage by 10%.
Blm can now flare adds multiple times, fire 2 on command, Thunder 4 (which does 230 potency to all adds hit) and foul them every 30 seconds for 650 potency with fall off. Pretty much outclasses Summoner's Aoes any time they want now.
Summoner's Aoe is heavily gimped on the fact that everything is a cooldown, has damage fall off, was nerfed in potency (dots) or requires aether stacks to be used. Bahamut has extremely awkward timing in fights and you can either use him as soon as you can, or hold onto him and potentially lose dps from Summoner's abilities just sitting off cooldown.
It's funny that you bring up Bard. Bard has two Aoes. Both 100 potency now. One has a 15 second cooldown timer than can be reset, the other is a spammable skill that does 100 potency. If You think Bard has the advantage, any class that can use spammable aoes that have more then 100 potency are at an advantage. Which would be anything except summoner with their 30 potency tri bind.
So out off the eight other dps classes, minimum of four classes can out perform them in Aoe. (Samurai, Ninja, Black Mage, Bard) Which also happen to outdps summoner is single target damage, and also happen to outperform their utility. Summoner doesn't even shine in Aoe even more. Literally no reason to have a summoner in your group when there are multiple classes that do everything better.
Seeing as most groups will probably have a samurai in their group their no point in having summoner. Just get a red mage or a black mage.