its not a mistake at all. fleet logistics and cost are not linked on a 1-to-1 basis and ships are balanced in context of every other ship in the game, not just against one particular ship. the logistics costs are also different by faction and reflect relative balancing of the ships available to each faction.
TEC: cobalts cost 5 logistics, javelis cost 4.
Advent: disciples cost 4, illuminators cost 6.
Vasari: skirmishers cost 7, assailants cost 6.
there's no one factor that explains why these numbers are the way they are, it is just the result of balance decisions made by the Ironclad development team.
you shouldn't be under the impression that long-range is just strictly higher level then light frigate, and therefore should always cost more. it doesn't work like that.