It is never the players or the manager, it's absolutely the organization. That might change now that Lerner's son is in charge but Rizzo clearly deserves blame too. Pretty rare for a GM to survive that many managerial changes.
People are ripping on Martinez as being in over his head in the same way they ripped on Kapler at the start of the season, I have a hard time believing Joe Maddon's longtime bench coach isn't 100% qualified, but since they are losing, easy target. OTOH, maybe those teams that refused to hire him up to this point found something lacking about his personality or people management skillls.
All that said Harper is clearly a nightmare. It would be hard for a guy like that not to be a prima donna, which is ultimately on his parents and his agent. But Rizzo made a choice to let that agent run the team, almost.