I've been testing the GC on the British side... I've started a few games both in January and August scenarios.
Every time the French and Spanish AIs have tried to break through the blockade using single unit stacks, sending them to every commerce naval box with the clear intent of raiding my merchants.
It's a sound strategy except that Athena is doing that with everything she has, including big Ship of the Line, and event troop transports! That translates in some very one-sided naval battles, as my fleets almost always manage to catch slower ships and destroy them piecemeal! It's not very fun and leaves me no hopes of fighting a big, Trafalgar style, battle. I've tried to tinker with AI settings, but this happens every time
Maybe the AI should be instructed to use only fast ships as blockade runners?