"According to the last reported numbers provided by Nintendo, Wind Waker sold 3.07 million copies worldwide, far below the 7.6 million set by Ocarina of Time.^[59] Aonuma would later comment in 2007 that he was "convinced the reason the Wind Waker did not perform well was because of its toon-shaded graphics style. It was something that you either loved or hated, and there was nothing that we could have done about it."^[58] As a result of Wind Waker's poor sales, Aonuma decided that "the only thing we could do was to give the healthy North American market the Zelda that they wanted," which led to the creation of the more realistic The Legend of Zelda: Twilight Princess.^[57]"

https://en.wikipedia.org/wiki/The_Legend_of_Zelda:_The_Wind_Waker#cite_note-NWR_13087-57

"Let me backtrack a little. As I was busy working on the connectivity project, it wasn’t as though the Wind Waker 2 project that I spoke of earlier came to a halt. Not at all. As some of you know, at E3 2004, we unveiled the game that would become Twilight Princess, the realistic Zelda game, and we announced that it was developed by the team that had been developing Wind Waker 2. Actually, there was a reason that that decision was made at the time. At one point, I had heard that even Wind Waker, which had reached the million mark in sales, had become sluggish in North America, where the market was much healthier than in Japan. I asked NOA why this was. What I was told was that the toon-shading technique was, in fact, giving the impression that this Zelda was for a younger audience and that, for this reason, it alienated the upper teen audience that had represented the typical Zelda player. Having heard that, I began to worry about whether Wind Waker 2, which used a similar presentation, was something that would actually sell. In addition, because we knew how difficult it would be to create an innovative way of playing using existing GameCube hardware, we knew what a challenge it would be to develop something that would do well in the Japanese market, where gamer drift was happening.

That’s when I decided that if we didn’t have an effective and immediate solution, the only thing we could do was to give the healthy North American market the Zelda that they wanted. So, at the end of 2003, I went to Miyamoto and said, “I want to make a realistic Zelda." Miyamoto was skeptical at first. I was so focused on changing the look of the game as being the solution we were looking for without coming up with a breakthrough game idea, and he advised me that “If you really want to make a realistic Zelda, you should start by doing what you couldn’t in the Ocarina of Time. Make it so that Link can attack enemies while riding on his horse using the Wind Waker engine, and make your decision based on how that feels." This is something that went against everything that the staff had been working on and I expected to come as quite a shock to the team. Surprisingly, my entire staff was enthusiastic about this change, and the project on which progress had slowed was given a much-needed jumpstart."

http://www.nintendoworldreport.com/feature/13087/eiji-aonumas-gdc-2007-presentation-the-fate-of-wind-waker-2

Official words, unlike your baseless comments.

Let's look at the series sales over the last decade:

TP: (Wii + GCN) 8.8 million

Phantom Hourglass: 5.1m

Spirit Tracks: 3.3m

Skyward Sword: 4m

Link Between Worlds: 2.7m

That is a franchise in decline.

And also, your personal opinion of whether it will be the best/biggest isn't really applicable to public perception.

So now you comparing sales of home console Zelda and handheld Zelda!? That doesnt make sense and you know it. I already wrote what I expecting from Zelda U, sales around 7m, so that means that will be one of the 3 best selling Zelda (definitely will sell better than SS), that and fact that ALBW will sell better than Spirit Tracks doesn't look to me like franchise is in decline.

Sales are telling real story!? Do you really think that Wii Fit, Wii Play, Wii Fit Plus, NSMB Wii.. are one of the biggest/best games of previous generation, because those games sold 3-4 better than The Last Of Us for instance!?

If you compare console to console and handheld to handheld, Zelda still diminished dramatically from Twilight Princess to Skyward Sword and from Phantom Hourglass to A Link Between Worlds.

And Wii Fit et al were absolutely among the biggest games last generation.