I do agree with all you said.
Fighting a fish for 8h is very unrealistic and yes something should be done about it.
I work on facts and the fact is 8h irl is 8 days in game and fighting a fish for that length of time would be impossible unless its a super fish and a super human fighting it, Both would die irl.
Angling stress occurs during the fish's fight after hooking. The vigorous physical exertion causes lactic acid wastes to build up in the fish's muscles. This in turn leads to blood acidification which can disrupt the metabolism of the fish. .The longer a fish is played, the more lactic acid is built up in the fish.
When your fighting a fish its not that it gets tired, its because of the lactic acid build up which stops the fish from fighting.
This is why when landing a fish it has to be done in the fastest way possible with causing as less stress to the fish as possible.
Once you have landed that fish after a long fight its important that you release the fish with care and making sure that after a long fight the fish can swim under its own steam.
If you fight the fish for too long chances are that the fish will die, either on the hook or while releasing it.
I don't know how your going to combat these times of landing a big fish but I suppose one way is extending the times for days so 1 day is longer than 1 real life hour, maybe 1 game day = 2 real life hours and after 1 game day the fish is tired enough to reel in ,but this would open up the problem of people using light gear to land massive fish just because they know that all they have to do is keep that fish on the hook for 1 game day.