Yeah, I like the line too. It’s the first crack we see in Vader’s resolve, furthered by his stare at the gantry window. I was kind of spitballing, as a lot of us seem to be torn about some of the dialogue choices in ROTJ. I saw that line appear on a few cut lists and was curious about where we stood on it. I’m glad we’re in favor of keeping it!
The Luke/Vader stuff doesn’t really need any dialogue trims.
I’ll agree that we don’t need to trim that particular line, but I do think that some of the Luke/Vader dialogue needs to be trimmed or altered. Vader repeating the line “You don’t know the power of the dark side” from ESB is lazy and doesn’t give us or Luke any new information, it’s an empty taunt at that point. “I must obey my master,” I’d argue, is a line that telegraphs Vader’s turn at the end in a more on-the-nose way than the “too late for me” line, and I think I’d be okay with its excision.