The difference is the writing. We were clear Emperor was feared in ESB and TLJ. We were also shown Vader was strong. Strong enough to kill Kenobi in SW and toy with Luke in ESB. When he had a conversion of heart, picked up the Emperor in a last ditch effort to save his son, and DIED in the process, we actually root for him. That my friend, was good enough to cover any illogical detail you may find in the original trilogy
I was going to write something about ep8 here, but I found that I could not care less about that movie. Ultimately it did not matter anyway.