It seems they achieve the same result about the universe's creation. I mean Pandeists achieve the same result about the universe's creation that Atheists or Darwinits achieve. Don't they?
Using the links provided by the OP, there are differences in concepts and results between pandeism and atheism.
For pandeism, the Wikipedia link states:
Pandeism ... holds that the creator deity became the universe (pantheism) and ceased to exist as a separate and conscious entity (deism holding that God does not interfere with the universe after its creation). Pandeism is proposed to explain, as it relates to deism, why God would create a universe and then appear to abandon it, and as to pantheism, the origin and purpose of the universe.
The result for the pandeist is a universe with an origin and purpose through a deity. The concept of the universe contains the idea of at least a former deity.
For atheism, the Wikipedia link states:
Atheism is, in the broadest sense, the absence of belief in the existence of deities. Less broadly, atheism is the rejection of belief that any deities exist. In an even narrower sense, atheism is specifically the position that there are no deities.
The result for the atheist is a universe with no deities either before or after its origination. The conceptual view of the universe contains no reference to a deity no matter how it originated.
This provides a conceptual difference between pandeism and atheism: one has a deity who became the universe and the other has no deities.
I will not consider Darwinism which could be reduced to a form of atheism especially as described by Alvin Plantinga. See his evolutionary argument against naturalism.
In general one should expect all theories to at least claim they conform to whatever the results are that we experience although their explanations and conceptual descriptions of those results may differ. They should all claim to be sufficient to produce those results or their theories would be falsified by the results.
That the results are achieved does not make the explanations how those results were achieved necessary. They would at best be sufficient to achieve the results, not necessary. Nor does it mean all the various explanations are the same.
"Atheism", Wikipedia https://en.wikipedia.org/wiki/Atheism
"Evolutionary argument against naturalism", Wikipedia https://en.wikipedia.org/wiki/Evolutionary_argument_against_naturalism
"Falsifiability", Wikipedia https://en.wikipedia.org/wiki/Falsifiability
"Necessity and sufficiency", Wikipedia https://en.wikipedia.org/wiki/Necessity_and_sufficiency
"Pandeism", Wikipedia https://en.wikipedia.org/wiki/Pandeism