I understand what you are saying. I do not think that would work in the same way. Drag clicking and double clicking are rule violations while things like camping or running can be part of normal gameplay depending on the situation with the game. Some players play the game in a defensive way or try to survive for a longer time and that does not always mean they are breaking the rules of the game.
Adding a warning like that could end up confusing the players or even punishing the playstyles of the game. Instead of a warning it would be better if the game of drag clicking and double clicking itself encouraged faster endings to the game like through mechanics that push fights or reduce stalling, in the game of drag clicking and double clicking.
I agree with you , as when cubecraft was at its peak some maps had the reputation of being a long game map which to be honest what made this game fun for new players (including me when i first joined the server) , looking back at 2017-2020 maps like under da sea and teaparty was widely knows most if the time of an hour long or more maps , which some players might not like it but some do . Thats why there are bows , ender pearls , fast pickaxes etc , its ok to be angry or sad about that but in that situation just make up a plan and try to find a way to win , thats where your knowledge in this gamemode could be usefull/improved , you learn how to adapt to each player playstyle and improve your skills in these gamemods .
Long games when you are competing and not dying in first 5 mins is what shows your true skill level and also alot of fun to play .
its also gives you time to learn more about the gamemode itself .