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Epiphini, I have a two-monitor setup, one is good and one is so-so. On a good one, banding is barely noticeable, on so-so it is quite bad. So it has nothing to do with your camera or lens, it's a digital compression thing.
Looking at histogram per channel, you will notice that the area with worst banding is the one where red is overblown. As you were trying to bring out red colors in sunset, you also over saturated red in blue areas of the sky, and low-resolution monitors are not able to correctly map the numbers. Try to process red areas locally in Raw processor with adjustment brush so it will not affect the rest of the image.