The AR, FAL, and M14 all have better control placement than the G3, and most find the G3's ergonomics inferior to all but the AK in the designs being discussed.
Please be more specific. Which controls? How about comparing the ease of selecting mode of fire for the G3 and the M14? On the M14, first tip the rocker switch, then disengage the safety to get on automatic. Two steps versus only one on the G3. Ever try to take a FAL off auto? Yeesh! Gotta pull that lever all the way back around almost 180 degrees to get it on safe, and you would need a thumb as long as ET's to accomplish it without removing your hand from the grip.
What is it specifically that "most find" about the ergos of the G3 to be inferior? The paddle mag release is about the only item that leaps out at me. Without it, the magazine release button requires ET fingers to actuate. Other than the paddle mag release, which is standard on the G3, but omitted on the civilian counterpart, HK91, the ergos of the G3 are quite well laid out. Seems to me that the lack of the paddle is critical, but deemed necessary to obtain permission to import the civilian rifle, so the lack of that feature in the context of this discussion is not relevant.
As far as sights go, for combat sights the G3 have no peer. So much more useful.
As far as what one does to a rifle after purchasing it to make it more suitable to his needs/desires, how does adding an ambi safety to a G3, or a paddle magazine release to correct a deficiency in the design of the civilian legal rifle, compare to glass bedding the M1a? How about unitizing the gas system on the M1a? Adding a spring loaded firing pin to the M1a for safety to prevent OBD? Perhaps reaming the flash hider on the M1a? Or exchanging the flash hider for one with a bayonet lug... an accession to governmental regulations sorta like the paddle mag release on the G3? What about the 1/2 MOA sight with hood that many install on their M1a? Oh let's not forget the 1/2 MOA windage knob. Then there's installing a plate and glassing it behind the front sling swivel. Maybe a heavy barrel?
There is no way, for a couple of hundred dollars more than the PTR91, you get all these things that owners of M1a's often do. A thousand dollars more, yes. Not a couple hundred dollars.