Because it was designed with a different focus? Yes. It's ignorant. IGNORANT.

Obviously no one is demanding some instant gratification every two steps. Walking a bit, even a lot of minutes in some instances, is required for almost any open-world game. Heck, there were moments in Red Dead Redemption (particulary in Mexico) where you could go with your horse for about twenty minutes and the only thing that would pop-up were some random plants and maybe a wild animal.

The problem here is balance. When you start playing you'll try hoarding every single thing you can get your hands on, so probably those first ten hours will be as joyful as any other, but with the extra of finding nice secrets and early-gear that will help your cause. What about when Link becomes OP? What about when you get unbreakable weapons, like the Master Sword (because I doubt that weapon can be broken)? What about when you have the ultimate armor? Will that balance still remain, or it will be a damn chore to get across the world and your only motivation is triggering the next story segment? Will Anouma make the world scale with you or it will become, inevitable, barren?

Look at Metal Gear Solid V, for example. The open-world does wonder those first ten/twenty hours, when Venom Snake is completely underpowered, Diamon Dogs is nothing but a bunch of unorganized mercenaries and you more often than not have to use enemy's equipment to get across a mission or else you risk going red numbers with your base income. You hoard all kind of plants, fulton all kind of animals, grab all kind of diamons in your path. But then you hit that point where you can basically destroy an enemy base almost without entering into it, because you can teleport, go invisible, capture enemies from afar and basically do all kind of weird shit that makes any point of exploration moot since nothing is going to top you there. And suddenly, a nice open-world becomes a damn chore, filled with inconsistent missions all across and all you wish was for some kind of fast-travel option that doesn't exist (There's one with the cardboards but it makes no sense and it's extremely limited), because you can't care for the world anymore.

Bigger than The Witcher 3 and Skyrim? Good for Zelda!
But it is going to be impossible for Zelda to top the awesomeness of The Witcher 3 and Skyrim.

Well this world is probably structured with each area being a different level like in older RPGs.  As for stuff to do, Zelda does have a leg up on other open world games, that being the dungeon design.  Whereas most dungeons in, say, Skyrim are purely combat focused and looting, Breath of the Wild's Shrines are like miniature Zelda dungeons with puzzles, enemies, and for some more meaningful rewards like runes.  These provide interactions that are fun on the basis of the interaction rather than just stuff to do to get loot.  And there's a hundred of them. 

As for becoming OP with unbreakable weapons and strong armors, so long as there are still areas that challenge you and there are still field bosses that you have to work hard to take down, that shouldn't be too much of an issue.  The Guardians look to be doing a good job of that as they are extremely strong and quite fast.  But a lot of this kind of thing comes down to timing.  When you get the master sword, when you get the ability to ride a horse, when you get your glider, etc will all be key to keeping things interesting, since those things will effect challenge and you traversal speed.  The fast travel system here is a good sign as it shows they are conscious of the size of their world.  Also, side quest content will be important.  It needs to be interesting on its own merrits. 

I will say one are this game has Skyrim beat in is traversal mechanics.  Much like Xenoblade Chronicles X, it looks like traversing will be fun in and of itself to a degree with all the climbing, gliding, shield-surfing, etc.

Your second paragraph is probably the most important one, and the one that should give off the alarm signals, because if Anouma struggles to create a world that scales with Link we'll experience the same problem all other open-world games end up having. While it's not that hard to try and maintain a balance, the fact that progression is dependent upon the player himself, as Anouma himself has stated, there's probably the fear of a possible void on which you advance too much for the sake of the world, leaving Link underpowered, or likewise try and grind for items and such that put too much of an advantage, which both cases end up breaking the pace and making the world less interesting and more of a chore.

Solving puzzles in dungeons is fun, by the way, but there's gotta be a purpose to that dungeon in itself. No one likes to solve puzzles without any kind of pay-off (and I'm not talking about the gratification of beating the puzzle per se, but the fact that the player should be loot-rewarded, like in Skyrim, if they want to give a nice incentive for players to keep engaging themselves in all these dungeons.

Will it have 70 hours of fucking amazing quests to do in the world also ? Like the witcher?