Why didn't Dalinar get the powers of a Stoneward when he bonded Taln's [Honorblade]?
Some readers have already figured this out, so I don't think I'm engaging in too large a spoiler to dig into this one here.
There are several oddities going on here. The most important one relevant to this question is the Blade in question. If you compare the descriptions of the sword described in the epilogue of The Way of Kings to the one that traveled with the madman (allegedly Taln, the Herald) to the Shattered Plains, you'll find they are different.
The one that the characters obtained in Words of Radiance is NOT an Honorblade. It's an ordinary Shardblade (as ordinary as one of those can be called.) I'm not going to say specifically what happened to the Blade Taln arrived with at Kholinar, but I will say that it IS a different weapon from the one in Words of Radiance.
The other issue here is the somewhat lesser question of whether this character is actually Taln, the Herald, or not. Some characters in-world don't believe that it is, though his viewpoint in Words of Radiance strongly implies otherwise. This isn't specifically relevant to the conversation for reasons I'll talk about below--but it is tangentially related. Because in the cosmere, Intent is important to many of the types of magic. It's theoretically possible to hold an Honorblade and not realize what its powers are, and therefore be unable to access them.
As an aside, this character was actually the primary protagonist of the version of The Way of Kings I wrote in 2002. A man who woke up, with lingering memories of madness, and claimed to be a Herald when nobody believed him--as he couldn't manifest any powers, seemed to have lost his sword, and lore said the Heralds weren't coming back anyway.
When I wrote the new version of The Way of Kings in 2009 or so, one goal was to focus the storyline. I'd included so many characters in the 2002 version that none of them progressed very far in their arcs, creating a strong setting and interesting characters--but a bad book. During the new version, I decided that this character would be moved to the later books, and I'd explore him there.
In the 2002 version, the text was very dodgy on whether or not Taln was a Herald. Confronting the fact that he might be crazy was a major arc and theme of the book--however, as I've worked on the new version, I've realized that it would be dangerous to be too vague on this. Stringing people along with the question for a book or two is one thing, waiting until book six or eight to do a character's arc, and leaving the question of whether they're a Herald or not all that time, seemed unfair.
So the text is going to be making manifest fairly quickly who this person is. You'll have confirmations long before we dig into his viewpoint in the later books.
So, a recap:
1) The swords WERE swapped somehow.
2) Someone could hold an Honorblade and not realize they had access to powers.
3) This character may or may not actually be a Herald--but the text is going to make the answer clear, and I'm not trying to trick you.