I think you are misunderstanding illusionism and the hard problem.

Illusionism does say that there is a conscious experience. So illusionism is convincing to many people who have conscious experiences.

The alien would be able to look at the computation and describe the conscious experience it has.

You could put human consciousness on an excel spreadsheet and it’ll still be conscious. Even Chalmers accepts a simulation would be conscious. So no that’s not a. Argument for p-zombies. Even people that use the pz argument don’t think that pz could actually exist.

But your conclusion is right, the simulation example does suggest that the consciousness in the hard problem doesn’t exist. Which just leaves the consciousness you experience explainable by easy problems. Which is the illusionist position.

Edit: and the hard problem isn’t just why there is consciousness. But why consciousness is impossible under physicalism. So in your post you are just actually referring to the easy problem of consciousness when suggesting it exists.