My recent experience:
I wanted a M14 battle rifle. Something accurate enough to take out threats, not some fussy paper punching wannabe. My accuracy requirements are sub 1 MOA of Bad Guy.
Turns out the M1A is more of a M14 tribute rifle than copy of a real M14 battle rifle. This was told to me by several folks on the m14 forum. Oops...
You can only shoot light bullet loads or you risk damaging/bending the oprod. Not good. They are a pita to clean (my opinion). I bought a Sadlak scope mount that sits cockeyed on the receiver because the receiver isn't milled right. I have a mill and digital touch probe and verified this.
As someone above said, it isn't as accurate as my LR-308, but that (308) is a heavy rifle set up more as a designated marksman rifle than a battle rifle.
I've been using a combination of grease and oil on my 1911s (and variants) for decades and hundreds of thousands of rounds and much prefer this to just some light oil. So using grease on a M1A was not a shocker to me. Makes sense actually.
Long(er) story short: I traded the M14 for a PTR-91 (US made HK 91) and some cash and am much happier.
Your experiences may vary significantly from mine...