Your descriptions of the organizational employment of a light machine gun or squad automataic in infantry units is generally correct, Mr. Irwin. The problem that armies have when actually operational is that casualties tend to wreck such niceties pretty quickly, although they will be adhered to as much as possible. The infantry platoon is where everything happens and is the "sharp end" of the army. I hear tanks get used now and then and they also use mostly the same machine guns. A "burst" to a tanker is at least 25 rounds.
Armies have struggled, in a way, with the concept of the rifle squad or section level automatic weapon ever since WWI. They all seem to have tried all variations at one time or another. The US BAR may have been the one in service the longest, with it being used for over 50 years. It and the M1 were still in National Guard units into the 1970s. There may be another that beats that record but I can't think of one.
The basic problems are that, at least at the infantry section level, is the conflicting requirements of mobility and firepower. If firepower were not a requirement, there would be no machine gun in the rifle squad. If mobility were not a requirement, water cooled guns would still be used. So all of these guns represent some form of compromise, just as all the others do. Yet as often as not, the man on the ground, usually with his nose on the ground (literally), will probably think the enemy has better weapons. Doesn't matter which side you're on. Sometimes both sides have exactly the same weapons.
For firepower, belt fed seems to be the way to go but it has disadvantages. Mostly the answer has been to devise some form of magazine for the belt. Where that has been done, the gun stayed. Where it wasn't, it didn't. There were probably other factors but it has always seemed to work out that way unless there were more varieties of machine guns actually used, as was the case in the US Army in WWII. The squad had the BAR, the platoon or company had belt fed light machine guns. The water cooled were at battalion or even higher.
All very interesting but why am I worried about this?
Shoot low, sheriff. They're riding Shetlands!
Underneath the starry flag, civilize 'em with a Krag,
and return us to our own beloved homes!
Buy War Bonds.