I honestly wouldn't have minded who Ian would choose in the end, but in terms of the plot/story, it made more sense for me that he chose TJ.
I know a lot wanted Jo for the end game but he actually has a bright future ahead of him, I didn't like how he was slowly coming to the dark side when he was with Ian. Their love was real but just not meant to be.
The author did a great job with the love triangle. When readers are divded on who should be the end game, that's how exactly it shoild be.
So this is basically esper and guide plot but they just used different terms which is ikigami and donor.