Along with the two really good answers above, I'll add these tidbits…
In your first example, UGLs are very easy for a trained soldier to operate in coordination with the rifle they are attached to.
Your second example is rather historically accurate as well. When the order to open fire is given, the first thing fired off would be the panzerfausts, which now spent are dropped (hence the reload rule - they have to get new ones out of their packs or left lying nearby). While the enemy is momentarily stunned by several nearby or direct hit explosions, rifles get shouldered from readied positions and a hail of lead goes down range in hopes of wiping the enemy out while they're still stunned.
Too often, gamers when given this rule, think it all happens literally simultaneously; questioning if the designers think soldiers have octopus arms, and forget it's a running chaotic battle where lives are on the line, and the will to survive along with training dictates you're going to throw the kitchen sink at the other guy trying to kill you.
In both my work as a CQB trainer for the military, and as a LEO, weapon transitioning training and practice is a mandatory survival trait. Often it's as quick or quicker to draw a secondary weapon as it is to replace a spent magazine.