No need to create or any new mechanics, they're fine as is.

There are parts I would adjust though.

The ACN when he hits his first 3 dungeons at level 15 has no real AoE, so tends to borrow Blizard II from BLM so he can contribute. At higher levels many do not use Miasma II, removing Bliz 2 from the ACN, and improving the potency of Miasma II along with reducing it to LvL 15 will go a long ways to remedying this problem.

Generally at 30th level the SMN will get BANE... his first AoE. Potency as follows...

Bio (40) + Miasma (35) + Bio II (35) per tick for 110 Potency AoE
Then much like at higher levels with Deathflare and Painflare... they will use something over the top. Generally this is Blizzard II spam (50 potency, cast time 2 seconds)... DoTs tick once every 3 seconds... spamming Bliz II is approximarely 75 potency every 3 seconds while spamming.

So at 30th the SMN/ACN does what is in essence...
110 + 75 potency AoE when combined for 185 AoE in damage per tick.

The BLM its sister class has the same type of AoE attack in Fire II.
100 + 20% per stack of fire for a combined 180 AoE per cast in damage.

Removing Bliz 2, and increasing Miasma II potency to account for it will both remove Excess Buttons, and give the ACN something useful in Party at lower levels. And will result in Miasma II actually being used more at higher levels as well.

The next Balance point is one where the Summoner Falls Short...

The 50th level Capstone ability for the Summoner is Enkindle. Which gives us...

Garuda's Aerial Blast (250 potency Circle AoE)
Ifrits Inferno (300 total potency Cone)
Titan's Earthen Furty (200 potency Circle AoE)

BUT only usable once every 3 minutes. Again I go to our sister class of BLM for this one.

The BLM has Flare at this level which is a 260 potency attack with the same +20% damage per fire stack. Usable at will and at any time but consumes all MP. Which is easily replenished with a single stack of Ice and a Transpose.

It is no small wonder why in ARR people abandoned SMN for BLM when THIS was the actual balance point at level 50. There is no justification for a 3 minute CD on Enkindle... this needs to be a 1 minute recast timer to bring it on par with Flare (and by extension Deathflare at level 60 which is usable once every 60 seconds due to the way Aetherflow works).

There's no real excuse or rational justification for it to be a 3 minute CD.

This also allows the Summoner to use actual Summon Powers a lot more in his rotation and will likely please the "Its not SMN enough for me" crowd who never played the job past level 50.

50th level to 60th...
Yeah both on par with each other. Here the BLM does more Single Target, and the SMN does more AoE... so the two begin to split off from each other as DPS jobs at this point... each taking its own specialization, yet still appropriately mirroring each other. I consider them both very well balanced against each other at these levels. The BLM runs into some problems at these levels but it has nothing to do with their actual damage output and more to do with content design literally excluding the Job from participation in various instances (linked to overdone mechanics).

60th to 70th level... aka the new Stormblood levels.

At this point no one can deny the Dreadwyrm Trance and Deathflare is the way the majority of players want to go with the Job... the Heavenward changes to SMN are incredibly popular, and Summoner flourishes as a job these days. I will propose a direction akin to what I hear from most SMNs who actually MAIN the job regularly would like...

More Aetherflow Stacks... and more powers akin to Dreadwyrm Trance and Deathflare (aka Bahamut's Teraflare).

Example:

Level 62: Another Aetherflow stack

Level 64: Another Trance like Ability that sets up the next power (or possibly skip this and keep it all under Dreadwyrm)

Level 66: Another Ability akin to Deathflare... but costing 4 Aetherflow stacks to use. Perhaps linked to Alexander or potentially one of the other Summons from Heavensward.

Level 68: Another Aetherflow Stack for 5 Aetherflow stacks.

Level 70: Another Ability akin to Deathflare using 5 Aetherflow Stacks... say Alexander's Time Stop ability for 3-6 seconds.

Why Time stop as an example?

Well one of the things I notice in high level raids... is that during the last 25% of health on the Boss Mob in the instance it tends to throw every mechanic in the book at you all at once... This is usually a critical time when you have the most Mechanics failure. And tends to drop a lot of people in the Alliance. So as an example if you've saved up your stacks and haven't blown them on a Deathflare... you can pop them for...

The Boss Mob and all Mechancs freeze for 6 seconds... the BLM runs over and places himself in perfect position and prepares Fire IVs around the multiple mechanics going off.

The Healers take their time while they have the shot to move out of the frozen kill mechanics and begin Raising the dead.

The Tanks pre position themselves to take on the boss again and perhaps critical time for a CD to refresh, pre prepping for the next mechanic.

Potential for a Raid save or potentially Tactical advantage late in the game just when you thought everything was lost.

And of course the Alexander Mechanic for this was pretty cool when it did it.

This is just an example of the things I both see and hear from others.