I might be sorely mistaken but I recall reading not too long ago that smn got a pretty sizable boost. Your summons actually provide party buffs or some such right?
The problem is that Summoner suffer from too many penalties.
Their advantages are the following:
Safe from getting hit.
Can fight without giving TP.
Can fight without gaining TP.
The problem is that these usefulnesses disappear fast.
What use is there in not getting hit if others are getting hit and the healer uses curaga? Same MP cost for healer, so there is no gain from this ability in a party setting.
What use is it to not feed TP if there is any other party member already doing so? This also looses all benefit in a regular party.
Fighting without gaining TP? Well, good in same situation as above. On monsters you have no other jobs dealing damage.
So take any random event and you are almost guaranteed to have no benefit from SMN only benefits.
Then there are the penalties.
Short buff durations.
Split on avatars so you never have access to all spells.
While a BLM pays MP for damage that can be resisted, SMN pays MP for damage that can completely miss.
Overall in any situation where you are playing Summoner, you'll be facing multiple of these penalties. Which is the whole problem with Summoner.
Imagine a SMN who paid ZERO MP for BPs, but still had a global BP timer. That would be roughly as unbalanced as allowing THF to SA from any direction. (Which really never was any big problem, SE just thought it was more correct to sneak attack from behind)
Imagine a SMN who paid MP for Wards that actually lasted 5 min each and had semi-decent potency. That would be like playing BRD, but have your songs last longer because you paid MP.
Imagine a SMN who could have a pet out doing nothing, and it had no perpetuation during this time and you could rest. No balance problem there either.
There are dozens of ways to make SMN less awkward and terrible without even nudging on balance. Question is why SE allows the job to stay at the bottom for so long, but then they haven't shown much skill at improving BST either.