It was the first step to arguably the most versatile individual rifle platform ever. The mil-spec standard is what created an industry that could support endless improvements for the user, including numerous cartridge/upper choices. Low recoil, huge choice of optics/sights, easy to maintain. Today’s versions are not the 60’s mattel guns.
Easy to maintain? Whatever. Any cheap ass POS that necessitates an anti-jam plunger and carries with it a few tens of thousands of dead Americans is no friend. Our love affair with the AR is ridiculous no matter how many silly toys you glue to the rail.