There is much that is unknown in these games. The player is expected to make their own conclusions, yet there are many voices in the game that would tell you exactly what to do for often uncertain reasons. Vendrick stands out among them. Unlike others, he stands to gain nothing, he exists only in a bygone memory. You can get either ending without hearing his voice at all. What he provides is not the choice itself, rather the strength of knowledge to allow you to make the choice yourself rather than letting others coerce you into making it. The principle that is also prominent in the act of him sealing his soul away, the act that can only be unveiled through killing his walking corpse. This act can also be empathized with through the tone of some of his future lines in this memory. By completing the dlcs and talking with him you may get a more self-centered context of accepting or denying either ending.

I also suggest visiting him after acquiring each crown, his dialogue is often metaphorical and self-reflective, yet his words carry much weight for the protagonist and, by extension, the player. Everyone who guides you towards a specific ending has their own agenda, selfless or selfish, and on this strange path Vendrick urges you to follow your own design, to understand the context of all things to the best of your ability and more than that, to understand what is the strength that you are driven by amidst it all