I don't think that's a good comparison in spite of surface similarities. Witcher 3 has, all in all, a very grounded and character-driven story which focuses on people and their motivations, and only deals with more abstract elements like the politics, witch hunts, Wild Hunt threat, or even the impending end of the world, insofar as the characters are affected by them. The Bloody Baron storyline only really works because of how him and his family are characterized; otherwise it's just a series of fetch quests.
PoE, on the other hand, wants to be a story about ideas and values, like PST or MotB, and I think a comparison with the first act of MotB would be more interesting. After all, both saddle you with a mysterious and troubling condition and have you seek explanations and possibly a cure for it. However, where MotB makes the curse a big deal to the point where an angry god lays siege to a city just to get ahold of you, being a Watcher means very little in practice. Hell, you have little reason to get involved with the whole Raedric problem in the first place. Maybe your Watcher powers should have somehow gotten you into trouble and forced you to participate in the power struggle (which is woefully underdeveloped in general) - that would also impress upon the player that his condition is serious and made the trip to Caed Nua more than an arbitrary checkpoint on the way to Defiance Bay.
I agree that the game is desperately lacking an emotional core, cheesy as it may sound. The souls gimmick is actually decently well-developed, someone obviously put some thought into what the implications of this kind of metaphysical arrangement would be, and came up with some varied and cool ideas. Problem is, they never moved beyond ideas and failed to construct a narrative around them, in the way that the narrative of Waidwen's invasion is expressed through Durance and Eder, for instance.
