He can be in many ads and pictures for the game, for most of the game it can be in his perspective, but no matter what, Link and Midna are the main focus of TP. Lets recap on these two suggestions you made.
The Wind Waker was an object being occasionally used for major parts of sailing and puzzles being used by the Hero of Winds. Without that object, it would be harder to sail or he wouldn't become the Hero of Winds and would most likely never saved his sister, keeping the seas covering Hyrule, and stopping Ganondorf from ruling Hyrule.
The Twilight Princess is a female ruler that keeps control of a realm that could be spread to the Light Realm with a deadly effect if not handle right. Unfortunately, a usurper made that happen and now needs Link (and Link needs her) to restore both realms to normal. Without the Twilight Princess, it would be a lot harder for Link to get the children that were kidnapped, harder to get out of puzzles that needs Midna's help, and harder for Link to defeat Zant and Ganondorf by himself.
Besides, Midna is not an object. She not even used for one purpose either. She can do many things that most side-kicks/major objects couldn't do in previous games, like teleporting you to other places, lock on multiple enemies while you were a wolf, holding and taking down heavy objects, guiding you through hard places as a wolf that most wolfs won't attempted, using the powers of the Fused Shadows for heavy ordeals, and (the old usual) hinting you what to do next and what weakness that enemies had. Not to mention she's deeply involved in the story's biggest ordeals.
For the last time, Link is a co-star of this game, not the star. Without Midna, then yes, he would definitely be the star of the game. However, she in it, she just as important as Link in the story, which makes them both stars of the game, no matter which role is more important than the other.