We are clearly in disagreement here, as I see every one of those points differently.
Stealing entire fleets is very hard today, and no rules are needed to remedy this. Skirmish yields low profit, and is "easy and boring", so this should not be the main avenue of a pirate. And FFJs will light many fleets, but all (except maybe one or two) will hardly give any profit at all, and those large ones will require huge fleets to defeat, which in turns comes with a cost to use.
I am not sure if we agree on what the consequences of this suggestion will be, or whether these consequences are desirable or not. I see the consequences being less dilemmas for traders, resulting in less strategy options for pirates, plunders giving FAR less profit than today, stealing ships becoming nigh impossible, and skirmish being the main - nay, ONLY avenue for the pirate.
I do not see how pirates can operate at all under this rule.