If luna engine is indeed causing the problem ,can you not :
reduce the number of monsters that spawn ,especially crawler waves?
implement a new turret that takes large waves quicker ,does less damage to heroic/legendary grade Mosnters for the sake of ballance?
remove luna daily completely ,increase rewards for luna weekly and keep it once a week,that is to say 8 + luna's light worth of drops?
implement an AFK prompt window?
look for more ways to deal with AFKing the instance in general?
There are many solutions ,introducing more randomness inside the instance should more effectively deal with botting (if that's the case) :
Waves can have mixed monsters forcing the player to fight instead of sitting with 100000 accounts opened in a corner waiting for sweet drops.
Since you can only use your crystals to spawn 1 type of NPC turret ,the turret could target it's appropriate monster while the player gathers more
crystals for the other type of turret.
Force some sort ot IP/Mac/HDD Serial restriction on luna ,in other words duoboxing should be the only allowed way,making it harder for people to
think of ways to run on more than 2 accounts at the same time.
Not sure how people do it. But say some prefer using their 3 single shot turrets and then go afk. If that's the case ,increasing the construction cost to
2 crystals ,while also keeping the same rate of fire ,but slightly increasing the damage to a single target could also be a solution to force the player
to be more active rather than sit back and do whatever (which they can still do ,however risk not getting S rank).
AoE skills from luna detachment transformation are limited to hit (in worst case) only 10% of the crawlers.
It's a difficult decision ,for us the players looks easy ,but 1 mistake can cause a riot in the forums just as we've seen most of the time.
Slightly reworking the luna daily seems the more appropriate step here.
Thank you so much for the EXP BUFF !!!!