I just went through this same research and decision process with similar objectives to yours. A moderate range plinker with a red dot optic that would also be suitable for defense.
Literally just went through this process, as in the parts haven't all arrived yet, so I may yet find out I hate something about it. But I had a good time doing the research and maybe my reasoning will make sense to someone else too. I figured out that some good things to have are:
1. Light contour, chrome lined barrel. A light barrel points faster and carries easier and the chrome is easier to clean.
I can't see well enough with a 1X optic to realize any accuracy improvement with heavy target barrels. Even if I could, I can't hold that steady anywhere except the bench. Higher heat capacity before failure is only critical for automatic fire.
2. Longer is a good tradeoff for me. A longer gas system is easier on the working parts and has more margin of error for reliability. A longer iron sight radius and higher muzzle velocity are good too. 16" midlength is better than 14.5" carbine and 20" rifle is better than either.
A short barrel and collapsing stock are very handy next to you in a vehicle where I'm not allowed to carry it or while dressed for a warzone in body armor which I don't have. If your idea of self defense includes inside the house then this answer would change.
So I bought a RRA A2 lower, a CMMG A3 upper with 20" A1 profile barrel, a BCM BCG, and an Aimpoint. I will see how this feels and make adjustments from there.