People who Opt into a battle and then use zero flag are making an aggressive move that negatively affect the rest of the team.
If people are automatically enrolled, it is a different problem. But this solution works for them also as they didn’t plan to enroll anyway.
In Either case, it is not so much a punishment to them for not using flags, but a reward for the rest of the team for using their flags that they are allowed to enroll in the following W3K event.
So instead of preventing people from enrolling if they didn’t use all their flags, but reverse it, and only allow those who did use all of their flags to enroll in the next event?
In both cases, what you do is with minimal coding changes, create an environment where people who understand teamwork can take raids to the next level.
If you do not understand teamwork, cooperation, and pulling your weight for the good of your team, you have no business being in this team event.
Either restrict future events based on unused flags, or only allow enrollment in the following event, if you use all of your flags.
Now, ask yourself what the goal is here. We want everyone in the event on our team to use all of their flags and hit hard. We want to win.
The problem is trolls who opt into the event and do absolutely nothing. It is doubly harmful, because you are matched with a team who has the same amount of people and they use their flags, so one person on your team not using their flags versus that same opponent also using their flags creates a Delta of 24 flags between the score boards PER TROLL who opts in and doesn’t use their flags.
So, don’t look at it as a punishment, but rather like a balance change to create a more favorable environment for those to Want to opt into.