Nickelback of 5.56 rounds. lol... i like that.
good sumamry... M193 is hit or miss with a 1:7 twist... same will do okay... most will be `4 MOA or even worse. out of 1:8 or 1:9 M193 will outperform m855 from an accuracy standpoint.
but agree with your assessment... M855 is the ‘do all’ round... jack or all trades, master of none.
*do all for 5.56... not do all round.