I've said it even before it happened: it was a mistake to make Summoner a job in FFXIV. They should have learned from how much trouble it caused them with FFXI and understood it makes even less in FFXIV's combat system (at least by the time of ARR). Summons should have been a general power mechanic open to everyone individually (like many Final Fantasy games) or a party mechanic (e.g., Limit Break in ARR).
The main issue is that conceptually the ideal Summoner job has too much to them. What people want in a single class that can command the most imposing enemies in the game (at least from a lore and often visual perspective), literal god-like beings. They want several of these, at least one for each element, and to make matters worse people tend to be gluttonous about wanting more and more summons (like in FFXI, even when the job was in shambles outside a few niches with several underused summons, the clamor for new summons was constant and loud). These god-like beings are expected to have their own unique abilities and attributes, ranging from the massive Titan and the magical Shiva. Melee, tanking, nuking, healing, etc. This is one job we are talking about and the basic demand is for it to be able to everything, because "bosses" do everything and summoners wield bosses. On top of this, there are the common issues that come with "pet" classes, essentially having the player control two characters instead of one, which can mean the very powerful trait of having twice the actions (or making the pet and/or the controller too weak to account for this). Even when done well, there's always a kind of awkwardness to it.
Now how do they implement this in a game that obviously can't handle the ideal? FFXI and FFXIV have two solutions, which more or less fail.
In FFXI, you do get the whole package (8+ summons, each with several abilities), but they were "balanced" by the fact SMNs were stretched so thin that they were pretty much good at nothing (and not even the real jack of all trades class). Avatars became nothing more than elaborate ways to cast spells (most of which were useless, but a few shined), harmed by a slow and unwieldy summoning system. When I was playing, they found a niche in the end-game by sidestepping one of the main aspects of the combat system, enemy TP generation. Similarly, when they weren't awkward replacements for better designed jobs, they shined in exploiting the game's weakness in dealing with their unique mechanics (e.g., fighting self-destructing bombs from a distance). Not very summoner-like and ultimately a net-negative for the combat system.
For FFXIV, first you have to consider that there's an overall design where all classes/jobs have pretty much the same number of abilities and traits (completely different from FFXI, which basically paid no intention to this, arguably to a fault). And now summons are not just neat side-bosses, they are the main boss fights of the game, each individually considered an endgame event rather than a member of a certain type of fight. And furthermore, they are inherently villainous, as a major part of the storyline/setting. Anyway, inspired by the constraints of the combat system (but not inspired enough, if you asked me), they went the opposite direction from FFXIV. Now you don't even summon avatars/eons/primals, but rather (evidently disappointing) simplistic figures of them. Because of how structured the combat system is (again, FFXI was a lot messier in how it gave out powers), they've only been able to give out three (and may take years of level cap rises before getting all six main ones, unless they do a huge revamp). They work in a heavily complementary method, minimizing the pet class issue, but also disappointing people who wanted a true "pet". While this is much more mechanically sound than FFXI's, it's much farther from the ideal.
So yeah, big mistake. I'd go as far to say it possibly shows a lack of understanding with the mechanics (the job/Armoury system, namely) inherited from the previous version of the game.
