The UPC logo variants weren't...generally...marketed according to their status as first or second tier characters. For the most part, the 20 packs contained the same mix of books, none more (or less) common than the other. The exception would be the boxed versions, which wouldn't have contained as many.
So, while sure, the regular versions of books would have been produced according to status...Batman, Superman, Wonder Woman, and the like...the UPC variants usually were not. If they produced, say, 10,000 of these books, they probably would have produced 10,000 of ALL of them, not 10,000 Batman, but only 1,000 Legionnaires. In other words...you're likely to find a much more even distribution among these much rarer (as a whole) versions. Detective Comics #0 UPC variant is likely to be "as common" as Legionnaires, etc.
The UPC logo variants were specifically produced to reach a different audience than the average weekly comics buyer.