It's all in the plate discipline. Walker, Caminero and Adell all have big tools and big time power, but their selectivity, or lack thereof at the plate is a huge problem. Of course all of them also strike out a lot, so it's a hit tool issue to some extent. Hard to be a good hitter with brutal K/BB ratios, even extreme cases like Javy Baez can only keep it up for so long before becoming a pumpkin.
Cruz and Schwarber walk a bunch, you need the third aspect of "Three True Outcomes" to still have a chance at success. In Jordan Walker's case he doesn't even get to his power at all. It's like if Vladdy was the same hitter except he also whiffed a bunch and never took a walk; gross.
Right now Caminero looks like the safest bet because his strikeouts aren't egregious, he's only 21 with potential 80 grade power. Walker is quite young also, only 23, so there's definitely a chance to fix him. Adell isn't a total write off, but he probably is who he is at this point. Probably puts up a random 3+ WAR season with 30+ HR once or twice and then reverts to being a pumpkin.