The deserter penalty was added to being kicked, because a long time ago tanks would use getting kicked to avoid dungeons they did not like at the time, considering then and now, tanks and sometimes healers have faster queues, almost instant for tanks.
The deserter debuff was then increased to leaving before the dungeon was completed, including being kicked, recently.
My suggestion is you want to do extra content in a dungeon beyond what a group wishes, to do so with a group of your own choosing.