Lux trade value is mostly coming from future control. Castillo has a lot more value in 2022 and probably 2023. It depends on how motivated the Dodgers are to win this year. Castillo is a top arm pitching well right now, not a future hope. I just don't see LA putting as much value on Future control when they can replace Lux over the winter by paying for whoever they want. The Dodgers will be vastly improved with Castillo and maybe the bigger thing is they won't have to face him in the post-season pitching for the Yankees or Red Sox.
I just don't see them prioritizing their number 9 hitter and a minor leaguer over a starting pitcher of Castillo's caliber. Especially if you include a guy with an .850 OPS to replace Lux. If I thought the Reds had any chance of signing Castillo, I wouldn't trade him for Lux and Pages.