Releasing something completely balanced is the ideal situation but weapon balance clearly isn't their strong point (yet). Apparently the recent NFAS and JG changes were fine and got pushed to live. Much rather have them balance weapons if needed be to ensure enjoyable gameplay regardless of release date. A balanced game requires all weapons to balanced, if other weapons get changed it could result in your weapon being more/less effective so it doesn't make any sense to limit balancing to after a year.
Besides that, why does a year after release matter? How fair is it if you buy a gun today that got released years ago and gets nerfed tomorrow?