I love both, the AR15 and the M1A. Come to think of it, I love most rifles.
I agree on the thoughts that you have concerning weight, which was part of the reason the services went from the M14 to the M16. Lighter weight rifle, greater maneuverability, easier to control, and the ability of the average soldier/marine to carry more rounds.
Another win for the AR15 platform in that you can change the cartridge by changing the upper assembly. If you are wanting a heavier caliber but still want to maintain the lighter weight of the AR15 you can swap the top for a 7.62x39 or 300 Blackout. You will not gain much in weight, still have the lower recoil, and have a larger caliber to put bigger holes where needed. Add to that, the fact that you can swap out parts very easily and make the rifle even lighter than it already is.
Chambered in the .223 Rem/5.56 NATO cartridge, I would hesitate to take big game, but change that to a heavier caliber cartridge and game on!
On 2 legged predators, most any cartridge will work but, again, I would prefer a larger caliber.