1. Ergonomics - The M1A is still just a M1 rifle with detachable magazines with respect to ergonomics.
2. Balance - The accessory rail is heavy and makes the weapon overly muzzle heavy. You still can't mount magnifying optics without expensive cantilever optics mounts.
3. Iron sight / red dot sight co-witness (if you run it like a CQB .30 caliber rifle as it was designed).
Apart from that, the M14 rifles and derivatives are generally pretty accurate, durable, and easy to operate.
With the availability of the SCAR 17S, I would not spend money on any other .30 caliber battle rifle if ergonomics, balance, and optics co-witness were important to me. All other .30 caliber battle rifles have weight distribution that is less optimal than the .30 caliber SCAR series.
I own a SA WWII M-1 rifle and I would not purchase or use any other .30 caliber rifle apart from the SCAR 17S. No other platform is as well-balanced, ergonomic, or otherwise "ready-to-run" as the SCAR.