Kiermaeir is a 3.3 WAR CF who turns 32 next year, so, not so bad. Still, he turns 32. Even at that, why would Tampa want Yadiel?
They are tight with what they spend and pursue value. Yadi is minimum wage for next year and the year after. Kiermaier is due $12MM next year and has a $2.5MM buyout for a $13 MM option in 2023. It's almost a pure money play depending on how you value hitting, D, and base running.
I'd say flat out that Yadi is a better offensive player. with 289 PAs vs. 387 going into today,
Yadi = .273 / .329 / .413, 9 HR, 7.6% BB, 20.4% K, 3 SBs
KK = .259 / .326 / .389, 4 HR, 8% BB, 25.3% K, 9 SBs.
Kiermaier is a vastly better defensive player, capable of playing CF.
The question then is, is Kiermaier worth an extra $14MM commitment for next year? I could see a low budget organization saying no, especially with Manny Margot available to play CF. Kiermaier is only worth that money if he is playing nearly full time. Yadi would not be a regular there, but i could see TB wanting to spend its money elsewhere and go Meadows / Margot / Arozarena across the outfield with Phillips as the defensive back up and Yadi being a cheap bench bat.