The M-16/AR-15 was designed by Eugene Stoner and he worked for Armalite not FN.
That's the first of the second-generation rifles (OK, actually the AR-10 was the first of the second-generation rifles, with the AR-15 being a variant of the AR-10). The two first generation assault rifles were the AK-47 (Mikhail Kalashnikov) and the FN-FAL (Dieudonne Saive). Both of these were originally designed to use an intermediate-power cartridge - the AK-47 used 7.62x39, and the FAL used the British .280 (7x43). I'm deliberately ignoring the MP-44 as it was something of a dead end - the concept was good, but nothing really evolved from the execution.

FN FiveSeven. A pistol with as much knockdown power as a .22Mag and I would never take squirrel hunting cartages into a gun fight where the other guy would have had the common sense to use a .45ACP.
It is designed specifically for the task of killing enemies wearing body armour. A .45ACP is incapable of penetrating most modern body armour/helmets. Thus, you're building up a strawman when comparing damage done by the round to unarmoured targets.

With what rifle? Even WW1 rifles loaded with striper clips never took that long. I don't care if he does not have mag pouches that is way too long.
5-7 seconds I can understand, but 10?

Under fire, at night, prone, in cover? Standing upright in broad daylight takes me about 3 seconds or so to change a mag, and another second to trip the bolt release and be firing again. Being prone and in cover slows things down a lot. Besides, that's all irrelevant to the point that even if mag changes take 10 seconds that's still fast enough not to matter.

Assuming that the rifleman is not under extreme stress and can take his time with his shot, then accuracy is the only significant factor in a successful shot.
Riiigght... We're talking about military rifles here, to be used by infantry in a full-on firefight. That means most of the time they're going to be hanging out of their arse with fatigue, and under a hell of a lot of stress from the enemy trying to kill them. Throw in the psychological factor that very few people actually want to kill one of the enemy (one of the major reasons ranges have moved from simple paper targets to falling plate ones) and accuracy goes massively down. It's becoming very obvious here that whatever experience you have of weapons is down to playing with them on a civilian range and maybe reading a few civvy gun magazines. The requirements for a military weapon are utterly, utterly different.

Bullet diameter does make a difference, granted the 7.62 NATO is overpowered for up close work, but urban battle also involves shooting through whatever the enemy is using for cover like brick walls, vehicles, sandbags, etc.
So use 5.56mm AP then. 5.56mm allows a much shorter and handier rifle which is controllable on fully automatic. That makes a huge difference in FIBUA as the chances of your first shot being on target are pretty minimal when snapshooting. 7.62mm NATO is not controllable on fully automatic by most soldiers (I have seen video of members of UKSF firing GPGMs from the hip on fully automatic and hitting the targets, but that's way beyond the majority of soldiers - the support staff trying the same thing couldn't even hit the hill the targets were on).
All that is necessary for the triumph of New Labour is for good men to say nothing whilst CGS.