A convoy that continues to scatter long after your initial attack is probably still detecting you. Ships that detect you 3Km away are doing so because you are not being stealthy enough and that is likely the reason you are getting re-detected. After the first attack, unless you are clear for another shot as they scatter and you're right inside the convoy, you need to slink away, then zoof at high speed only using radar contact for position. Or without radar occasional-brief visual contact of the outside elements, get way out in front and slink in again. By then they will usually be reformed (mostly) but will also be more alert than the 1st time when you caught them off-guard.
If the game was as bad as you claim, no one would play it. It's all about tactics, technique, stealth, surprise, survival. Put yourself in the position of the convoy captains. What would you expect if you were them?
-Pv-
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