Worst part is how incredibly short-sighted these elves are.
Let the dwarves have their time with the otherworlder... who have short lifespan and can't transfer their skills.
The dwarves would have a slight boom in artefact creation, on a limited scope at that because they rely on a couple of individuals, and a few years later they can't do anything anymore because the people necessary for the crafting die of natural causes.
This would then demonstrate how unreliable isekai crafting is in comparison to the elves'.
In comparison, the demons are a more lasting threat, but they don't seem interested in competing with the elves.
Elves have very long lifespan, make them act like they do. Make they play the long game. That's their strongest advantage.
So any animosity towards the elves and their eventual demise will be entirely caused by their own actions.
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For the sake of the shorter timespan of the story, have them point this out: "Your actions are futile. You might be enjoy your ride now, but these otherworlders will eventually die. Everyone does. Then, the whole world will see that nothing is more reliable than elvish craft." Then they can use social manipulation to leverage their already considerable influence against the budding competition, pointing out to existing customers how the new dwarven+isekai products are flashy but unsustainable. Better yet, encourage them to try and get their hands on the otherworlders. Delegate, keep their hands clean. They are above committing petty crimes themselves.
Instead, immediate violence is their answer. This is a waste of an otherwise interesting premise.