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I get what you mean - I think a lot of the stuff like taxidermy, rock carvings, dinosaur bones, may well work best when it is a distraction/diversion/break from the story, as opposed to stuff remaining once you have finished the story... that said, a quick look online to investigate a few things I wondered about (ie, the 'Strange Man' from RDR1) showed me there's a few things I hadn't triggered (a Nite Folk stranger mission in Bayou Nwa/Bluewater Marsh, for example).
With hunting I have usually just chanced upon things rather than go looking for them specifically - only did 3 of 6 satchels as a result, only found 1 panther (2 *) and 1 bison (that early camp honor mission in Chapter 2) and still not gone to the Iguana island near Rhodes... Haven't used bait or anything as I just forget it exists. I suppose the huge leap in number of species (there were only 36 or something in RDR) doesn't make it easier...
I think I've sunk nearly 100 hours into it and only once or twice questioned whether I was making the best use of my time.
as soon as I finished the epilogue I stopped playing after a couple of hours and never came back to it. despite being a completionist the world becomes very boring quickly once the story goes away imo. the hunting pretty much obligates you to look up animal spawns online as things only appear in certain spots at certain times and circumstances and as you can buy all the satchels in the epilogue there wasn't any real point (plus they're pretty much obsolete by then anyways).
Was also disappointed when I saw how devoid of content a very large part of the map turned out to be too during the end game. having seen the full map early on I was expecting to have a lot more to do.
and replaying the missions resets all your stats and equipment to a super low level making them much harder and 10x less fun.
haven't even been mildly tempted to try online either after seeing how rockstar have gated all the interesting shit behind a ridiculous grind for gold bars or micro transactions and read how much griefing goes on.
i might replay one day as it's a great game but will do the more grindy tasks much earlier on in chapter 3 when the world is more alive.