To understand Anakin, it would be helpful to understand the way in which a Jedi is trained. From what I gather in the OT, Luke’s training begins with Obi-wan telling him to trust his feelings. This preliminary part of training gradually opens the initiate’s mind to the Force, allowing them to go as far as even levitating small objects. Next, the student augments their skills with rigorous acrobatics training and exercise. At some point, the teacher will use some method (like the Dark Side cave) to determine the student’s greatest fear. With practice, the student is able to face this fear in their mind. Finally, the student’s training is complete with the construction of a lightsaber. However, this doesn’t make them a Jedi. The final test of a Jedi is to confront their greatest fear in person, if possible. This test is ultimate, and is pass/fail. There is no running away. Either the student conquers their fear through the use of the Force, or they die. If they use the Dark Side to achieve victory, they must be killed. Yoda’s warning about fear is well placed.
The problem of Anakin can perhaps be solved by recognizing the effect this training could have on students and masters. What if the student’s fear is great, but reasonable? What if the student fails in their final test, but understandably so?
What if Anakin were to realize that his greatest fear was his own death?
When the test of a Jedi is against an enemy, the test is simple. When it is against death itself, how can any test be devised? Ironically, the Lucas Prequels have almost this same test in the character of Palpatine. If Anakin destroys Palapatine, he is severing the temptation to use the Dark Side to become immortal. Since he cannot destroy the promise of immortality, Anakin falls and becomes Darth Vader. This aspect of the prequels, if seen through the lens of the ‘Final Test’, succeeds. Anakin doesn’t even need to commit evil acts. His fall was the ultimate irony - saving a life. However, through the lens of this test, it is essential that Obi-wan kill Anakin, but since Anakin’s fall is entirely human and reasonable, Obi-wan is massively conflicted. The Mustafar duel could play out essentially as it does in the prequels, and over the next twenty years Obi-wan would try to convince himself that Anakin was indeed ‘seduced’ to the dark side by Palpatine. Anakin and Obi-wan are both tragic characters in the end, and when Anakin destroys the Emperor, he finally makes good on his test to become a Jedi.