He's been in a prolonged slump hitting for little power with lots of Ks while being awful defensively in RF. He's just not a contributor at the MLB level right now, certainly not in the outfield.
Vlad had generational hitting talent, never had issues with strikeouts, and unlike Walker completely dominated the minors. Walker's 128 wRC+ in AA last season as a 20 year old makes for a great prospect, but at a younger age Vlad was making a mockery of the upper minors. They're not that comparable. And believe it or not, Walker's groundball rate right now is worse than Vladdy's has ever been at the MLB level. 60%, barf.