Again, I would politely suggest this is an overly emotive response. If someone doesn’t want to play with you, move on. There will be someone else who does. You can frame it as cheating or any other way, ultimately it’s because someone decides to exit the game rather than play it with you. The difference between a legitimate exit (by FDev’s) definition and the illegitimate exploit is an arbitrary timer. The difference of 10 seconds seems, to me, barely relevant. Out of curiosity- are you fine with someone exiting via the timer but not by logging out? And if so, how do you know the cloggers you have encountered haven’t exited legitimately?
Imagine you play a match of football (soccer for the ones across the pond) and then you kick the ball towards the goal and in te very same moment the goalkeeper realizes he can not block the ball they say "STOP! We don't play anymore!" which basically ends the match. Not only is this poor sportsmanship but also a waste of the other's time. Granted, it may not be that much of a waste as the match probably would have lasted for less than 15 seconds but still.
The argument that a players decided to simply not play with/against other teams/players doesn't count because the decision has been made when selecting a gamemode. In our football example it would probably be a decision between single palyer training, home training against obstacles and dummies and a real training against another team from the town. In Elite, it's simply solo/PG/open.
Upon selecting solo play, the player decides to not want participate in any other player activity.
Upon selecting PG, the player(s) decide(s) to participate in a selected player activity.
Upon selecting open, the player decides to participate in any other player activity.
Note that the decision being has consequences. In solo it is denying all player activity regardless of preferences whereas in open it is allowing all player activity regardless of preferences. In PG players create their own, likeminded environment to player together in a specific way (for example showing new players the game and doing an educational session).
Now, exiting the game/mode using the 15 second timer is not a bannable offense. I am of the opinion that the timer needs to be significantly longer and refresh when recieving damage (regardless of mode or contact (PvE/PvP alike)) but according to the rules it is not a breach to log out using this method so a combat logging report is not required which means that this method is totally fine.
Terminating the game to bypass the timer is, however, strictly against the rules and there are some easy ways to detect the difference between a legal way of exiting the game and a prohibited one.
One out of many ways is to watch someone's movement. When the player in question is not showing any user input for 15 seconds (slows down, only flying in a straight line, doesn't fire unless they have turrets, etc. etc.) then it is very likely that he has been logging out using the timer method. However, suddenly vanishing the second the shields drop in a proper PvP fight for example while still doing active manouvers a second before is most likely a termination of the .exe as you can not give any user input during the timer method (which is intended).