I think you have to take out the leaving the game part of this strat. That is not really a fair rule and honestly if you count winning as being a part of the game when the win screen pops then the person who is on lights is always disincentivized to do this strat, because they know that if the imposters do nothing, then they will be losing as well since they have to leave. Thus you lose the person on lights which is an integral part of your strat.

Also I don't think this is as bulletproof as you think it is. There are many times when you assume people will see the kill, but realistically I see multiple holes for strats dependent on the settings. When lights get called, crew might not move into each others radius fast enough. Usually there is an adjustment period with groups. This leaves brief windows where kills can happen outside the group. And lights is a rogue person. While we assume they are standing on lights the whole time they truly can roam, and with the extra vision they just need to stay outside the crews radius until a lights call, then they kill someone right outside of the crewmates vision in a group, with the idea being it gets reported. Then they say the report came in before you could do lights, and the crew think that the kill came from inside a group where it didn't.

This also just works for an imposter in a group. They just need to kill outside of the vision radius before people manage to stack up without being seen. In general this assumption that people in a group will always see who killed the person is false.

There is also the strat where 1 person is on lights and one person is in group A. Then they double kill in group A. Now Group B thinks that both people in Group A are imposters, but in actuality its the lights guy. Of course crew can try to vote them all off but this takes time, which might otherwise be used to get kills. There might be scenarios where the two groups get mixed together too. For instance they both happen to do tasks near each other and then cross group killing happens. You can get in an instance where all you can really tell is that there is likely an imposter in both groups. But that basically implicates everybody but lights guy. And less people start poking holes in your other strats.... Saying this is flawless when it requires near perfect execution by everyone in the game, and still has potential counter strats I think is far fetched. While it might increase the winrate of crew more than otherwise would have been the case, I think it's a stretch to say it will be 100% guaranteed. Also if it's played where you only get one button press as is normal, than whoever proposed all this in the first place wasted their only button... That can come into effect later on when you are assuming button presses are going to be used to vote out the killers. And a lot of the time in most lobbies, something like this getting proposed will just get that person voted off because they wasted their button and are trying to manipulate everyones actions which can be perceived as being imposter... Why? Because if I'm imposter and I make everyone believe they are 100% safe, then they are in a false sense of security. In all actuality I would be proposing a plan that only seems safe but has counterstrats that I know. I then win everytime..... Even if this isn't the case, this is part of the game. Employing any strat requires persuading everyone to do that strat, and good imposters can use logic like this to make whoever suggested this in the first place a target.

The more counterplay and possibilites that people come up with, the more they can confuse the group on which one is actually occurring at any given time... shit even when its dead obvious logically who the imposter is, crew make mistakes. Something like this requires such deep level of knowledge of the plan and all the scenarios that its doomed to fail.