For the simplify-plugin, all examples in the reference have choice-elements with maxOccurs="unbounded", which correctly results in List-properties. But if maxOccurs is not specified it defaults to 1, so there should not be List-properties but singular fields.
Example:
<xs:complexType name="typeWithElementsProperty">
<xs:choice> <!-- maxOccurs defaults to 1! -->
<xs:element name="foo" type="xs:string"/>
<xs:element name="bar" type="xs:int"/>
</xs:choice>
</xs:complexType>
should rather result in
@XmlElement(name = "foo", type = String.class)
protected String foo; // no List!
@XmlElement(name = "bar", type = Integer.class)
protected Integer bar; // no List!
for usage of <simplify:as-element-property/>