Correct. I'm just going off what can be gleaned from the article and slight extrapolations.
I didn't say -only- bosses will be fought in 3D. I just said bosses will be fought in 3D. Important distinction there. Frankly, any more than that would be even more negative.
If you take mechanics from LoS and put it into a 2.5D game, it becomes more like a beat em up (which is what 3D action games are more like in 2D space). I hate 95% of all beat em ups. Sounds problematic to me. It should even concern anyone who wants even a more classicvania-like approach, since classicvanias were still for the most part 2D platformers--not 2D beat em ups.
It's still a negative for me if a game doesn't. Whether the game can make up for that on other issues is another matter.
This describes pretty well what is "wrong" with this game. A side-scrolling "beat-em-up" is not that appealing a prospect when you're looking for a game that feels like a real Castlevania game. That being said, I'm all for the game even like this, cause it'll be a new experience. I just wouldn't want all future handheld games to go this route, but I'm sure they won't so I'm fine. This also may be the best format to give us a Castlevania in stereoscopic 3D, so I'm hyped actually.