A 3 Kilo mangrove jack would absolutley sh#t all over a 3 kilo cod, mangrove jacks are the hardest fighting fish in an estuary pound for pound without a doubt, and around structure will give an angler far more stick than a sluggish old cod.
Yes, what your saying about cod is true in regards to their 'Torque' but a jack will dust up an angler in no time, whilst a cod will inhale a bait and cruise slowly back down under a snag for dinner time. Although a cod is a reasonable fighter, you'd have to say a jack around the 3 KILO mark would do over a cod in most peoples books.
I have no doubts that a cod around 20 kilo would definitley pull someone around in a canoe very easily, but just imagine if a mangrove jack could reach that size
, although its not possible as the bigger specimens move offshore and the record for one is around 15 kilo from memory. But if a jack was physically able to reach that size in an estuary it would probably be the most feared fish by any angler
Thats my opinion anyway
Cheers
Morty