FA is NOT “needed” because of the design of the BCG, the indent you see on the BCG through the ejection port is there so you can push the bolt forward if needed, if the bolt needs more than finger pressure get it into battery, ramming it forward with the FA could cause worse issues.
With all that said, I prefer a FA on my ARs because they are “normal” to me, the non FA uppers were before my time and the FA has been there as long as I can remember, BUT I also understand the negative issues the FA can cause and I have attempted to train myself to use it properly.
Funny side note, when I explained what the FA was and how to properly use it properly to my wife, she literally looked me in the eye and said “then why is it even there if it causes more problems than it fixes?”, my answer was “because people who would never need to use it thought the gun needed it”, she says “well that’s stupid....”, yeah, indeed it is lmao