Miami is the more prestigious, older and more "famous" tournament between IW and Miami, even though they are "technically" of the same value (draw, ranking points etc.) so I disagree with you here.
If we say assume that Miami and IW are the same, then one extra Slam final for Djoker compared to Fed should give Djoker the edge this year anyway.
If you use that argument, you need to apply the same criteria to the majors. Wimbledon is the oldest (first championship 1877 compared to 1881 for US Open) and most prestigious in the eyes of the players and media. It's still played on its original surface, players still must wear all white, etc, etc.
Do we agree that if Djokovic won the most important Masters 1000, then Federer won the most important major?