It really depends.
The thing that Fallout 4, and Witcher 3 doesn't have is good, well thought out game mechanics. It really depends. however, on how Zelda U is going to change up Zelda.
Really, this is a good spot to be in as well, as Fallout 4 took a bit of a Skyward Sword approach with the "One large step ahead, two steps back" approach. Witcher 3 is absolutely amazing... However, there are great opportunities for improvement. We are also forgetting the fact that Xenoblade X has toppled these two games in the many opinions of the reviewers of the game(and released as previews). If Xenoblade X can topple these games, despite coming a lot later than intended, than Zelda U has a chance of that within itself.
Really, at the end of the generation when we look back at the generation, we will really only remember Witcher 3, Final Fantasy XV, Xenoblade Chronicles X. Zelda Wii U needs to compete with these games. I hope that they cannot only match, but outdo these games.
I genuinely believe Zelda U was delayed because of the Witcher 3. Had it released in the promised year, it would have been absolutely underwhelming. It was going to be a smaller game, Witcher almost undoubtedly utilised mechanics and ideas that would make Zelda U seem outdated, Nintendo are no longer the pioneers in gaming preferring to rehash and update a little on their past exploits rather than improve significantly and set the trend. Of course the graphics in the Witcher 3 are next gen whilst the Wii U can give us something like you'd get on the PS3 or 360. The majority of gamers prefer the Witchers look and since Aounuma wants to appeal to a wide audience, I think he probably believed he wouldn't get that and nobody would be interested after the Witcher 3 and those that were would have been disappointed.
Now with the extra time I think they will at least have a game that matches the Witcher 3 in gameplay whilst having its own unique aspects however minor. If they have gone against current trends and been smart, story will have been prioritised and storytelling, which was very good in the Witcher 3.
I agree that this was probably the reason of the delay, and that is very smart. I think that Zelda Wii U would have gotten TP syndrome, where there was a huge world, but not much to do with it. I am glad that the game was delayed for this reason. I am also excited to see the gameplay possibilities, however, we have seen so little that it is impossible to say.
However, regarding "rehashes". Nintendo does not only rehash, these "rehashes" were only because of the Wii U's struggle, and them wanting to pump out a game quickly. However, games such as Splatoon, Xenoblade Chronicles X, Super Mario Maker, and Pikmin 3 are no mere rehashes. They are either something completely new worthy sequels, or new games/ip's altogether. You also fail to mention that these "rehashes" are not Nintendo exclusive... I mean, this has been a huge problem this entire generation. Yet the fact that Aonuma is willing to take his time with Zelda U means that he wants to make it something different.
Furthermore, regarding graphics. The system doesn't matter, the effort, time, and artstyle matter as well. Xenoblade X, for example, is yet another example from this. Polygon states that
The Wii U may traditionally be thought of as underpowered hardware compared to PlayStation 4 and Xbox One, but you wouldn't know it when looking at
Xenoblade Chronicles X. This upcoming role-playing game from Nintendo and Monolith Soft is massive in scope and utterly gorgeous.
whilst Gamesradar states
Xenoblade Chronicles X may be a Wii U game, but it has an identity, a look to it, that is unlike even the most beautiful high-resolution next-gen games. You'll wander across an impossibly large steel ring half-buried in the desert continent of Oblivia and wonder who built it, how it got there, where it came from. You'll climb to the tallest mountain and take a running leap into the lake below just because you can. You'll gaze into the night sky and marvel at the half-dozen or so moons hovering above. You'll wonder about the history of this planet - who was here before we arrived? Who created these structures, and for what purpose?
This is downright proof that the Zelda team could make something look amazing that could match Next Generation Games, and that anything below that would be pretty disappointing. Aonuma should be trying to make, downright the best looking game this generation, and I hope he holds himself to that standard.