I didn't say that fear was Palpatine's Achille's Heel.
"Fear ultimately proved to be Palpatine's achilles' heel as it caused him to constantly plot and devise schemes against his enemies."
That describes the 8's deterioration to 5.
"They [8s] think that they will be able to maintain their power by being shrewder and more premeditated. Instead of acting recklessly, they will attempt to act with more foresight [especially using the Force to see into the future]; by being more secretive, they will be able to strike without warning [such as the result of Windu's attempt at arresting Palpatine]; by being more wily, they will be able to hide from their enemies until they are ready to defeat them utterly [Palpatine spent years hiding his abilities as a Sith Lord until the moment was ripe]. In short, the temptation for Eights to go to Five lies in the union of power and safety, a seemingly unbeatable combination [and it was unbeatable for becoming Emperor]."
Personality Types.
Your passage about 8 describe Darth Vader. Not Palpatine.
You confuse being mischievous with 5ness and 8ness. 6s can be mischievous and calculating.
The stressing point is wrongly interpretated. It means that 8s find stressful and have a hard time to be frugal and repess their guts like a a 5, but can disintegrate to that point under severe strees. That's what happened to Anakin/Vader, who is a true 8.
However, Palpatine is not "stressed" when he acts like a 5. He does that easily, it's his confort zone. His plans took decades to be achieved but he never had problems or found stressful to be calm and patient. He started to be afraid when he had to truly take action and fight.
This Achilles Heel shouldn't be confused with the Achilles Heel of each e-type, such as Pride for the 2 and Anger for the 8. The article obviously wasn't delving into the enneagram. Not that it doesn't apply to Palpatine. He is an avatar of the unhealthy 8.
The article decribed the Palpatine's personality and doing this, the passion of Type 6. Artists create characters and they have a personality type even when they don't think about that especially. But if we follow what you say, George lucas was sitting in his harmchair and thought "hum, yeah, I will create Palpatine as the avatar for Type 8, but he will be a very fearful and coward 8". Obviously, that's not credible.
His main passion is for using anger and aggression to release the powers of the dark side.
Just like every sith. That doesn't say anything about his enneatype. However, Darth Plagueis used his fear of authorithies to make him balance to the dark side. Anakins isa true 8 and he not afraid of anybody.
The enneagram Achilles Heel of Palpatine is anger, hate, and aggression.
No. He control that too much well to have that as Achilles's hell. He simply know and like to use it when it's time to do.
He refers to them constantly when attempting to recruit new members to the dark side, especially with Luke. It is through these - not fear - that Palpatine attained both triumph and defeat.
He refers to Luke's anger, not his anger. However, Palpatine is never as much in anger than a true 8 like Palpatine is.
The Achilles Heel of the Jedis on the light side is love. By repressing the need for love, by attempting to act like Monks, they have blocked themselves from appreciating and releasing the full power of the Force. When Luke defeated Anakin in battle the true power of love was revealed for the first time in Jedi history, only it was not romantic love but that between father and son.
What you say here has nothing to do with typology.