The original Legend of Zelda game was more influential and important for the video game industry than the original Super Mario for the NES

Super Mario Brothers is a side-scrolling obstacle course type game In which the objective is to run and jump your way through various "worlds" to free Princess Toadstool from the evil King Koopa.

 The Legend of Zelda is one of the first "open world" style games, the objective is once again to save a princess, but this time you do it by obtaining the fragmented pieces of the Triforce by salvaging them from the dungeons hidden throughout the land of Hyrule.

The keyword here is "open world". Mario is a great franchise, but Mario is objectively less innovative in the gaming industry than Zelda because Zelda was one of the first console based open world game series in history. The first Zelda game trail-blazed many open world gaming mechanics and while it is definitely a great and classic game, the original Mario game did not "raise the bar" in the way Zelda did. 

Mario was based on a classic, linear side-scrolling design which was implemented in many games at the time. Mario was a very original concept, but was little more than a creative way to implement gaming mechanics that had mostly been used before. Zelda on the other hand was the grand supreme Magnum Opus mystical Godhead Nirvana-sent Bodhidharma of the gaming industry at the time. It was the first true open world game, and was among the biggest and most fleshed out  game-worlds  that had ever been seen by the likes of man at the time.

Here is an image of the over-world of the first Zelda game, keep in mind there are also 9 dungeons of varying sizes plus several caves hidden throughout Hyrule.

Here is a map of the dungeons.

Con cannot provide an argument because he loves Zelda and plays it every day and he can't find a single thing wrong with it.

Zelda is your favorite game. You couldn't deny it any longer.