So yes, tell me more about Luke skywalker Wrath™ upon realizing that his father is basically a slave in the Empire and to the emperor and how much torturous the suit is. It's for nothing but pain and feels. Gosh, we're all palpatine in secret.
This is the only time I’m ever okay with being compared to Palpatine. :P Give me pain and feels.
Okay, so when Luke realizes this, he’s understandably angry and would love nothing more than to go put a lightsaber blade through Palpatine’s black, shriveled heart, but he’s smarter than that. So he bides his time and plots in secret. He works to get his father proper medical care and does what he can to tweak the suit’s inner workings to be more medically ethical. They can’t do a lot, because they can’t afford to raise Palpatine’s suspicions, so things on the surface have to stay the same. They have to be careful to work around failsafes, and not trigger alarms because you know Palpatine has tamper alarms in that suit.
But they get it so that Vader isn’t in 100% constant pain, and he can breathe on his own for a short time, enough to probably get him to an oxygen mask or hyperbaric chamber if they need to. They manage to disable the killswitches on his suit, so it can’t be shut down by remote anymore.
Luke does what he can to help build up his father’s self-esteem and self-worth, though it will take years of therapy and love from his son to really make a dent in his cycle of self-loathing and break his childhood conditioning that Palpatine has reawoken for the last twenty years. But it’s mostly Vader/Anakin’s desire to see his son safe and free that gets him motivated to act. Luke reminds him, both with simply his presence but also his words, that Vader has choices, that Vader is a person who was once known as Anakin Skywalker and can be again. That Vader is the father of a beautiful, loving, kind boy named Luke, who believes in the goodness in Vader’s heart and his ability to do the right thing.
Basically, Luke channels his rage over his father’s situation into something useful and healing, and he and his father kill the Emperor together, breaking his father’s chains and freeing the Galaxy in the process.