Honest question. How did we go from "the greatest battle implement ever devised" to inaccurate heavy garbage by simply changing the capacity with an easier to load box magazine and a slightly smaller and lighter cartridge?
A case of everything is relative? M1 was the hotness for it's time. The enemy then caught up and surpassed thus the successor rifle was now inadequate? FAL envy?
The M14 isn't garbage. It is a pretty good 1950s service rifle. The fact that it can be made to shoot to match standards is a happy side benefit. The fact that a 1950s technology service rifle that is being used as a match rifle requires a lot of upgrades and continuous attention to do so isn't surprising. The M1 sure did and does. The FAL and G3 aren't match quality. The M14 in spec and with good ammunition will shoot more accurately than either but really the issue isn't how tight any service rifle shoots, it is how reliable it is, and does it have repeatable service accuracy? Yes the M14 does.
The M14 suffered from poor production standards by HRA and to a lesser extent, Winchester. HRA turned out barrels that were way out of spec; Winchester produced parts equally out of spec. None of that helped the reputation of the M14 in the early days.
The M14, FAL, and G3 were obsolete the day they were each introduced. The Brits had the right idea but the wrong execution with the EM2 and .280 (7mm) intermediate range rifle. Except in the Boer war and Afghanistan, there was no need for 800 yd capable rifles when virtually all combat engagements happened and still happen at 300 yds or less, and most within 100 yds. The Brits learned that lesson by then end of WW2, but we ignored it. Thus the M14.
The T44 (M14) wasn't even the rifle that Ordnance was championing in the 50s. The new service rifle was supposed to be the T25, but when it couldn't get over the hurdles, the T44 which was in the background, was rushed forward and pushed through accelerated prototyping as the competitor to the FAL.
All that said, the M14 and the M1A are fine rifles for what they are: heavy wood and steel rifles firing heavy cartridges that shoot out a long way. They last a long time and take a lot of abuse. Just ask this user.