"Did I leave anything out?"
No. You're absolutely right. Things are perfect the way they are and are in no need of modification or thinking "outside the box".
The 6.5 Grendel is a superior round to the 5.56, the 6.8SPC and the .308. It fires a long, thin bullet, which makes for a very high ballistic coefficient. That means it bucks the wind better, making it both more accurate than other rounds and allowing it to retain more energy downrange. The Grendel actually outperforms the .308 past 500 yards in terms of energy delivered to target, and isn't much behind closer in. The lighter weight means that a soldier or a squad can carry far more rounds of it than .308 for the same weight, or the same number of rounds for less weight. Check out http://www.65grendel.com/ for more details about the round, its development, available uppers, etc.*
6.5mm bullets are routinely - and very successfully - used on deer. As such, they are good man-stoppers as well. The 6.5 Grendel, having been developed from the PPC family of rounds is an inherently very accurate round. Specifically, the 6.5 Grendel is an evolution of the 6.5mm PPC optimized to seat 107- to 130-grain match bullets at an overall loaded cartridge length of 2.255 inches (gee, what a coincidence, that length will fit the mag wells of the M16/M4/AR15 family).
Check out http://www.65grendel.com/art001devnotes.htm for notes from the perspective of a shooter who came up with the idea for the Grendel, and from the round’s designer.
* Note, I do NOT work for, or have an interest whatsoever in, any of the companies that produce or sell anything related to the 6.5 Grendel. I just think that it is the best round out there in a practical size, and that it should seriously evaluated by our Armed Forces.
You think so? I don't.
I like the performance of the 6.5x55 Swedish Mauser round, but how can we make it just a little slimmer and keep the speed up? I think the new .270 round this weapon is featured with is a good start.
What's needed IMHO, is considerably more penetratation than is accomplished by the 5.56 NATO combined with a relatively flat trajectory and all in a compact round. This will require a very high pressure round, and a strong, reliable, lightweight, compact weapon. NO easy task.
I know you were using sarcasm BTW. I surely didn't want you to think I was so dense as to want to keep things as they are.