In addition to this, for tactical and limitation reasons, could I perhaps suggest that FTL can only work either from the edge of one system to the other, meaning the OUTERMOST areas, and from the outermost areas to any point farther into the system, as long as there is a relatively clear line of sight [meaning you can't go through something like an asteroid]?
And FTL inside the gravity well of a planet, meaning anywhere near a moon, would destroy a ship?

That way people can't just LEAVE if they start losing. The Valkians did, if you read earlier, warp into the outer edges and work their way inward.