How about using a hash? The main problem here is that any original order will be lost, but maybe that does not matter?

#!/usr/bin/perl -wl

use strict;

sub create_list {
   my @skip_dbs = @_;

   my %hash;
   @hash{qw/fetch forward user smtp/} = undef;
   delete @hash{@skip_dbs};
   
   return keys %hash
}

my @list = create_list("user", "smtp");
print "@list";
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