Get some freethinkers who have been there and done that many times and know what the abuses a primary and secondary firearm may be exposed too by your average Mk 1 Mod Ohhhh shoot and scoot Soldier, Sailor , Airman or Marine.
As in .......why do we seek just ONE ?...........:o)
As you well know each environment and each enemy poses a different threat and problems that must be addressed initially and as the threat changes.......When we were dipped we packed the M4 w/ M203, a M1A, a MP5SDA3 and a 12 ga shotgun as well as a 1911A1 or a Browning Highpower in fly away kits and took what weapons we needed when threat briefings were disseminated.
Modern logistics will provide for more than one weapon system IMO for the modern DOD fighting troop !
There's no 'ideal' weapon. It's a fantasy. They've all got plusses and minuses.
In some cases the ideal weapon for the job is going to be a Barret M82, in others, a 1911 or a Hi-Power. For 'housecleaning' duties the MP-5 is just about perfect, but you've got to get to the house that needs cleaning first. Under fire from hidden assailants firing AK's, the MP-5 is just about useless.
They're all some sort of compromise.
Perhaps what is best is to decide on a small 'suite' of weapons and then make sure our front line guys are expert in ALL of them.
But that means more training and more ammo stocks which means more money and a bigger logistical trail which means.....
Well you get it.
Just my two cents.