Agreed. Elvis was a grown man who made his own choices and who is ultimately held responsible for his demise. However, I can look at milestones big and small that Elvis came to in his life that, if under the influence of someone other than Tom Parker, I feel that his final scenes would have played out completely differently.
For instance, if Parker would have allowed Elvis to play in the film 'A Star is Born' (the part was instead given to Christopherson, who used it as a great means to further his own career), Elvis' acting career would have taken a completely different turn. He would have been led to other great roles no doubt and his own personal morale of where his life was going would have improved. With an improved morale, he wouldn't have turned to (as many) prescription drugs. Its a long, complicated, and winding road, but the littlest of details (had they been handled differently) could have changed his life, and quite possibly saved it. It was all about the little things for Elvis- the smallest of details are what literally shaped his life.
Now having said all that, Elvis was no doubt far before his time. There was no standard by which to compare him to. Motion picture and musical artist today know to stand up for and protect their rights as free moral agents from the oppressing and edacious minds that are akin to Parker. Today's artist can look to situations like Elvis' and see what worked and what didn't: Elvis had no one to look to for such examples. He was the one that set the standards for so much of the entertainment industry as it is today. With such an epic beginning and entrance as this was there an almost predestined and inevitable need for an exit to be just as epic, however tragic and heart wrenching as it may be.