Enjoy Summoner before it gets nerfed...

[Fyce]

The problem here is that SMNs have the strongest burst between all classes,

Sorry, sir. That one would go for the melee LB.
Yes, it's a burst, and no, it's not an exception. It's used to "remove" a battle high enemy and/or a healer from the battlefield. IT's also faster and easier to use than the SMN's combo because all melee have a stun and gap closer. If a SMN starts his combo and his target runs away, the combo fails completly and the SMN won't kill anyone.

usable from a distance,

Yes, that's the point of a mage job.

completely istant,

Not at all. (RS) > Tridesaster > Painflare > Fester > Energy Drain > Transe > Deathflare has roughly a 4-5 seconds setup. It adds up if you have to use Aetherflow and another Fester, Painflare or Energy Drain to secure the kill.
It takes even longer if you have to use Sprint to catch up a running target which tends to be at max range and running.

It's more than enough time for a decent healer to throw a single heal and make the SMN very sad.

with a relatively short cooldown

1 to 3 minutes cooldown (because of RS and Enkindle). During that time, a SMN without stacks is completly useless. An annoyance at best.

and with no risks or penalties whatsoever;

The risk is to fail killing the target because of a heal, a stun, the taget being out of range, etc. The penalty is, if you fail to kill that target, you're a useless piece of living 5 points for the enemy team and you better run away and /sit because you're no longer useful to your party.
No other job become that useless after failing to kill a target.


Please, at least, try to play the job once before making any assumption.
Everything you said was incorrect in some way (except for the "It's ranged", which was an obvious and 'duh' statement).