Yes, reading comprehension is a dying, if not lost art...
interesting to me, in the RIFLE forum, in a thread asking what 4 RIFLES...
that so many people said 12ga shotgun....
Sounds to me like the OP has it pretty well covered already.
For a long range "reacher" for antelope and deer, many said .270 Win. My personal preference would be the .25-06. IF you handload, a 6.5-06 is even better, and both have advantages over the .270.
Lots of folks said .223, and if you are wedded to the AR platform, its fine. But if you are looking at a bolt gun, there's nothing a .223 does that a .22-250 cannot do, and some things a .22-250 just does better than a .223.
There is a huge amount of overlap in cartridges, and so there really isn't any wrong choices, just some that are more versatile, or better for a specific application than others.
Things like ammo availability, different action types, etc are important factors when choosing what best for your situation, but are meaningless when discussing the merits of specific cartridges and loads in comparison with each other.
Flat trajectory is also meaningless when discussing the round's performance
after it hits. And before it hits, all flat trajectory does is make it easier for the shooter. Flat shooting rounds are more "forgiving" of range estimate errors (when shooting at big game size animals especially). For instance, if that deer/antelope/elk, etc was actually 350yds away, instead of the 275yds you thought it was, a very flat shooting round could still be a clean kill, where a very arched trajectory round might be a wound, or a clean miss, under the same conditions.
For those who know their round's drop, AND accurately know the range, flatter doesn't mean a lot. It's when you think your are right, but aren't that flatter helps most. And that's why we like it!