How does that solve the problem? You can't declare an array of strings inside a class, either.
You can annotate the method as `@return array<array-key,string>` or even `@return list<string>` (array of strings = indexed via anything that can be used as a key in PHP vs list of strings = indexed via incrementing integers, starting from 0). I guess the OP suggestion was to use Arrayable / Iterable interfaces, which would work as well, but would require more effort (= yes, declare a class)