Shamanism is in goblins roots. In the early days before goblins became super intelligent, they were very tribalistic and living with lots of exposure to zandalari trolls. It makes sense how they can be shamans. Plus modern day goblin shamanism seems to incorporate some aspects of tinkering in it.
Shaman are unique in that they’re the only class in the game that has to make a bargain with an intelligent being to get their power.
Priests and paladins call on the the light, but the light isn’t a real being and it doesn’t care whether the thing you worship approves of your actions or even exists.
Warlocks make deals with demons but that’s for the assistance of the demon itself. Their fel spells are just spells, and they could be used without the demon’s cooperation.
Even Druids just learn how to Druid from Wild Gods. They don’t get any kind of power from them. Just knowledge.
Shaman on the other hand need the constant approval of a being other than themselves in order to have power. Which means they need to make a deal. Goblins are the kings of one-sided deals.
They are more like geologists - they understand the elements and can know how to best exploit them. Where do most geologist work irl? Fossil fuel companies.
Aight when you think about it, Goblins are the elements most reliable servants. Those little buggers are willing to anything for anything valuable - and how how do you think it is for a fire elemental to make a diamond, or for a water elemental to whish up a pearl? The elementals don’t care - they just want their bidding done. As goblins usually don’t want anything more than riches, they don’t have to worry about being killed for their power, being used as recources in the creation of an ascendant, or ESPECIALLY about any of their servants morals.
Goblins are the best elemental servants. Just not in the scope of the world. Remember that the elements, if they weren’t balanced, would be more than happy to destroy the world at any time.