How could or should the 6.5 mm Grendel be improved?

[stanc]

The 7mm UIAC is too much like the .280 British (7x43).

Actually, it has little in common with the .280 British, which had a long, streamlined bullet and short, fat case. A more accurate comparison is to the .270 British (7x46).

While I like the 7mm, it does have more recoil (heavier bullet) than the 6.5mm. The one thing that is coming out from my research is that the 6.5mm is at the optimum point among calibers. It has the sweet spot in terms of BC and sectional density.

However, 6.5mm lead free bullets may not have sufficient mass for the terminal effects required of a GPMG.

This whole question would have been moot had the US gone with the .280 British and the FAL back in the '50s!

Nah. The 5.56x45 cartridge and M16 rifle would still have been developed and fielded, for the same reasons they originally were. So we'd still find ourselves in the same situation as now, at least with respect to rifles and carbines. But, let's not get sidetracked into a futile discussion of what coulda, woulda, shoulda happened.