It is said that Darth Vader's body armour suit is a direct upgrade of how General Grievous was created. But I can't understand how this is an "upgrade". It was heavier, immobile (compared to Grievous), wasn't as agile, and as far as we knew from the movies it didn't have gadgets like grappling hooks, etc.
So why was it considered an upgrade? Surely the Grievous armour was a much better killing machine.
I don't know where you read/heard about Darth Vader's suit being an upgrade to General Grievous.
In Wookieepedia, the section for Darth Vader's armor: Discomforts and limitations:
Having had so much experience with mechanics, Vader was dismayed by the incompetence of the medical droids responsible for his resurrection in Sidious' laboratory on Coruscant. The technology in the suit was already obsolete, having been used to rebuild and create General Grievous decades earlier. While he retained his knowledge of the Jedi arts, he began to feel uncertain about his place in the Force, and while he had taken his first steps toward awakening the power of the dark side, he felt uncertain about his ability to sustain that power. He knew that he was hampered by his injuries, and knew he never could achieve his full potential because of it. At times, Vader wondered if Darth Sidious had purposefully designed the armor to restrict him.
It doesn't seem to be considered an upgrade at all.
It is likely sidious would have wanted to limit his abilities out of fear that Vader would become more powerful and kill his master, since this is the way sidious himself became Lord of the sith by overthrowing his master
