I thought Ken’s thank-you was essential.
I throws the audience into thinking he might need help going home and shows Ken’s world view to be utterly twisted by his Master’s teachings.
He genuinely find’s Han’s sacrifice to be ‘helpful’ and thanks him sincerly.
That’s really F&*ked Up! In a good way.
That’s my issue: the only reason Kylo would say “Thank you” is because Han did something that was helpful. The struggle was the moral and emotional decision, not the physical distance. Han made this struggle more difficult to overcome, so a “Thank you” feels out of place.
If there was no emotional struggle and Kylo just walked up and stabbed him, a “Thank you” would be a perfect line.