Well, a lot of other Zelda games are sprinkled during that cycle which are often great, and the end results are usually critically acclaimed, so i don't see a problem. However, i do feel they could manage their time better.

First HD open world and art style, are only two thing that I mentioned, again from some reason you dont see all things that I wrote or you dont see want to them from some reason, you just keep mentione only some of them, but my point all those things combined clearly justify 5 years of development.

Again:

Finding completely new, unique, great and beautiful art style and graphics, and finding and implementing completely new mechanics and staffs, and developing very complex dungeons and epic bosses, all that for open world adventure game with NPCs that is developed by team which in same time working on other projects too, and we add to that Nintendo obsesion of releasing very polished games with no bugs or any problems, so all that together clearly justify 5 years of development. If we talking about Zelda U, will add to all that that is first HD, true open Zelda with bigest world by far than in any previous Zelda games.

Also Zelda series is unique and very different series than any other series on market, you can't say same for Uncharted, Killzone or even Skyrim, and that certanly also is afecting on devolpment of 3D Zelda games.

Summary:

-Finding completely new, unique, great and beautiful art style and graphics.

-Finding and implementing completely new mechanics and staffs.

-Developing very complex dungeons and epic bosses.

-All that for open world adventure game with NPC.

-First HD, true open Zelda with bigest world by far than in any previous Zelda games.

-Developed by team which in same time working on other projects too.

-Zelda series is unique and very different series than any other series on market and that certanly also is afecting on devolpment of 3D Zelda games.

-Nintendo obsesion of releasing very polished games with no bugs or any problems.

So this is very obvious, but again you dont want too see, for instance devolpment of Zelda U cant be compared with any other game on market, not even close. I just keep telling that all those things combine clearly justify 5 years of development, but you again just mention few of those things and you saying that does not justify.

Again, none of those things are particularly demanding except first HD game and open world, and those have been done before in 4 years.

Here's the problem with your theory; the game was originally slated for a reasonable 4 year cycle. But by Aonuma's own admission, he derailed the entire production to go chasing after new ideas instead of completing the task at hand. 

Not only just first HD true open game with huge world (you never mentione that world is huge), but also in how many Zelda projects Zelda team was involved this gen while they were working on Zelda U, too many.

Well we cant be sure about that, maybe they delayed Zelda U because of NX port, but certainly even if that is main reason why is delayed, they will certanly use that time to implemente some new ideas and make even better game, than it would be if it was released this year.

And again, becuse next Zelda will not be their first HD, true open game with huge world, and becuse of new unifed platform, they could make new NX Zelda for around 3-4 years, but if they pull again MM, for 2-3 years. So in worst case I expect to see Zelda NX in 2020.

Implementing new ideas won't necessarily make it a better game though. For all we know, it might have turned out better if they'd stuck to the original plan, since we don't know what these new ideas he wanted to pursue were.

Well its not only about new ideas, they will certainly improve and polish whole game while in same time they implanting those new ideas. For instance Zelda U world itself will have more staffs, NPCs and quests than it would have if it was released this year.

One of those ideas probably crossed their mind when they worked on MM 3DS, It's very interesting that delay was announced after MM 3D launch, around same time when delay was announced we had info that Mask Salesman will return in new Zelda game. But personally I would love seasons mechanics, but Mask mechanics are always interesting.

Thats one of reasons why I think Zelda U will be great, becuse while Zelda team worked on Zelda U, they were involed in OoT 3D, WW HD, ALBW, MM 3D and TP HD devolpment and they probably taked some of the best things from those games and implated in same way in Zelda U, with certanly some completly new staffs and mehanics. I am pretty sure that Aonuma dont calls Zelda U "Ultimate Zelda experience" with out any reasons.

http://www.nintendolife.com/news/2015/03/the_happy_mask_salesman_is_teased_for_a_reappearance_in_a_new_zelda_game

They'll certainly have more time to work on it, which usually is a good thing, but not always. It's possible to overwork something, for instance. Or to add things that just weren't needed or don't gel with the rest of the package. Maybe the original vision for the game would have turned out better than the revised version being worked on at the moment. Until we find out exactly what these new ideas were, we can only speculate.

Maybe, but in most cases dealays makes games better not reverse, so I dont have any reason to suspect that will be different in Zelda U case.

There are many, many cases of delayed games turning out bad. Duke Nukem Forever, Perfect Dark Zero, Spore, Conduit 2, Metroid Other M.

Yes, delayed game doesnt mean that will be good eventually, but almost certain that will be better after extra time for developing and polishing.

I dont think Zelda U will be bad in any sense, after delayed I certain that will even better game than it would be this year.