The overvaluation of Castle by basically everybody who desperately wants Fox in San Antonio is hilarious. Now, I'm not saying Castle is going to be trash - if we believed he was hopeless we wouldn't insist on getting him - but the idea that after a half a season of "dude can't shoot" he's an untouchable piece when his team is in pursuit of a star in his prime who will be there long term is silly.
As an example, do we think Devin Carter has the potential to be a very interesting player? Yes. Are most Kings fans loath to include Carter in an arbitrary deal? Yes! If Carter were the sticking point for, say, a Markkanen deal, is he on the Jazz? YES!
Castle is a young player who remains a lottery ticket, and I'm sorry Spurs fans, but he's a part of the price of business. You're not trading for Kevin Huerter here. If you were, I'd get it. But you're hypothetically trading for De'Aaron Fox. You're already winning the trade. You're going to have to give up some value. Sorry.