No, it isn't an exploit when an individual player leaves a guild and join another, but when several guilds collude together to pool their resources/members to win a planet, it is an exploit. Scenario: The allied guilds decide that for a given week they will help Guild A win Planet X. Members from the allied guilds take turns joining Guild A, run Conquest events (lockouts, WZs, etc.) and then leave Guild A. Then other players from the allied guilds join Guild A and do the same thing. The next day the same scenario is repeated, and so on for the duration of Conquest week. It is cheating and most certainly is an exploit.