As most games, storywise the end is rushed and chopped up.
E.g. they ruined the crones, great villains and a bit of Ravel in them, by making them servants of the wild hunt (wtf???) and easy killable.
Because they needed some sort of closure.
Also Keira Metz best waifu.
Witcher 3 in general feels weirdly rushed in the story department. Everything surrounding Ciri is obviously a late development addition as neither her gameplay nor story sections seem to be actually finished. Her gameplay is just stripped down Geralt with teleport dodges that obviously cover too much ground to be practically useful(outside of that one endgame boss) and no signs(which is fucking bizarre because Ciri was explicitly trained to use magic by Jennefer). Those sections are also miserably short and not communicate anything that could not have been said in dialogue.
As far as the story goes her entire presence appears to have been hastily tacked onto the story as the vast majority of the game is only loosely connected to searching for her. Most mainline quests in fact connect to her via a brief cutscene or an offhand mention that have no bearing on the plot at all. Worst of all the whole "search for Ciri" quest ultimately resolves it self via a obvious deus ex machina, again almost as if unfinished or tacked on at the last minute. Especially in context of the previous two games where nobody even bothered to mention Ciri by name(spoilers: because her story was already fully resolved in the books and bringing her back made no sense even if Geralt had all his memories) its just bizzare to suddenly make the whole game revolve around her and stopping the White Frost.
Which BTW was up until Witcher 3 clearly presented as a natural ecological catastrophe(like the sun dying) that is simply destined to happen far into the future either way and had nothing to do with Ciri or elder blood but was exaggerated by prophets who had no real idea what they saw. Hell, the whole story of Witcher 1 was clearly written to establish that Ciri and her elder blood are not as rare or unique and that others might possess it as well(a.k.a Alvin).
It smells of rewrites or just plain desperation as the release date was getting closer and the game was only 50% done.