If SMN had even half of the things it could do in other FF games, the cries to nerf the job would reach the heavens and echo across the world. AoE Stoneskin, Aoe Blink, AoE stat increase to the full party, AoE heals, party invincibility, and one-hit kills, to name a few. The complaints about RDM would look like a drop of water on a hot anvil by comparison.
Started as affliction, then tried to make them Demo locks with DWT (back when demo had Metamorphosis).
The problem with summon variety is that you have a high risk of overlap unless you design each egi for one specific purpose. And even then you start running out of room fast. FFXI's SMN ran into this problem, leading to more convoluted ways to use summons over time. And some summons are just stupid-powerful in-world, which makes it a balancing nightmare. For example, Alexander with Perfect Defense = AoE Hallowed Ground to a full party; imagine the shitshow that would create if our SMN could do that. Or if Titan-egi could Stoneskin a full party at the cost of an Aetherflow stack.
My beef with SMN is that design-wise it's all over the place. 1-50 was "DoT mage with a pet", then 51-60 was "fuck that pet, trances a go-go", and 62-70 it seems to have gone fullretarddragon mage or "we've replaced the egi with a mini-bahamut; let's see if he notices". There's other issues like unresponsive/inefficient pet AI, lack of connection between master and pet, and how the role primals play in the game has changed.