Have you flown your MIS much? One of the things I don't understand is when it says "2x S3 - 6". I'm presuming this means 2 launchers, with 6 S3 missiles total, or is it 12 total? This matters, because the MIS can be made somewhat stealthy by removing the exterior pylon mount missiles and putting Void Armor on it.
The MIS is unusual to start, because it has S3 in the rotating auto-loader, but what is the time between launches? The missiles themselves have tracking lock times, so one supposes after waiting for a missile to come available, the Arrester III still needs 3.2 seconds to lock before you can launch again.
Personally I would want fire support for a Prowler coming from ships an opponent can't see. If an escort ship can see a missile launching ship at 10 km, the player will be tempted to immediately go after it. Really the best thing is for the escorts to spend a few seconds indecisive, choosing between the fire support and the Prowler. That time could be enough for them to die. If they go after fire support that is 10 km away, they will necessarily be gone for minutes, which is enough for the Prowler to drop 3 teams of 5 boarders and exit the scene. Then the missile-boats leave and whether the escorts are still alive or not, they have failed to protect their charge. So having the missile-boats off screen due to extreme range and perhaps limited stealth is really handy. It will force defenders to look for what they cannot see instead of firing on the Prowler.
S3's fly much faster than fighters, so they can attack from extreme range and have decent travel times to target--about 1 second per km. S2's don't have enough range, and require about 50% more signal to lock, so no good at 10 km (with the exception of the Rattler II.) S5's are too slow to attack escort fighters with. They're for bigger ships.