Remember how long ago it was when an AR15 meant the long 20inch barrel and it was virtually impossible to find an M4 style firearm.   AR15 firearms have come a long way, both the upper receivers and the lowers.   Trying to find a firearm now that does not have staked parts or is not chrome plated is getting harder and harder.   Even the machining on bolt carriers has improved to the point that Direct Impingement firearms are 10xs more reliable than before.  All you have to do is pop the bolt carriers out of the guns and you can feel the difference.

Even the average AR15 now is a minute of angle firearm and can still run like a military rifle.   Barrel technology on your average AR15 upper receivers has doubled and tripled.   I have an LWRC M6A1 rifle that supposedly has a barrel life of about 7500rds but the newer ones are close to 20,000rds.   The bolt carrier group is a  one piece unit and there has been absolutely zero broken parts on it.   Hopefully the only things that will eventually where out anytime soon are the extractor and springs.  It’s always wise to keep some of the basic spare parts around no matter what AR15 you own.