Give or take some flexibility on what you count as "great," neither Kb nor Javy has been a great player since leaving the Cubs.
The further a guy gets past 24/25, the less reliable their greatness is, and you already have those years locked down under the cba for anyone you develop.
Obviously you have to spend the money on something eventually, and free agents aren't guaranteed value either, but waiting as long as possible for more information increases your odds of hitting. If I'm paying for a guy's age 28-32 seasons, I wanna see 26 and 27 first, not commit to it when he's 25.