All the players you mention (except Bony) are just better players than Soldado and would (and indeed have in some cases) perform well in any league they might play in.
I think football is more random than people imagine. All that really happened to Soldado was that he missed a few chances in his early matches and lost confidence. AVB did a reasonable job in showing faith in him to little avail but then Sherwood came in and selected Adebayor instead which must have been a real kick in the teeth. Then Kane turned into a miracle man so Soldado remained on the fringes and never got his confidence back.
To be fair to Sherwood he attempted to revive Soldado and partnered him with Adebayor in games, while Soldado had chances and simply couldn't perform but they did link up well together.
Soldado was here for 2 years and much like Veron (a player given every chance) it's not about luck, it's about a player adapting to a new league which some simply can't adjust to.
Certain players can switch leagues and instantly work, players like Beckham who was slaughtered at times for having average technical ability, yet he played to a high standard in three top leagues, he was confident in his ability to settle, something Soldado lacked from the outset.

