Headshots don't matter with the Executioner*—just aim for the CoM
Seriously? I just assumed they did since headshots did more damage, or so I thought.
If it doesn't have a sniper rifle that can 1-shot a NPC from 3Km distance, instantly, the hardened FPS players consider it to be pants...
That's a straw man fallacy right there. You're really taking the criticism to the extreme. If you look at what I've posted, I've presented a perspective that is far more middle ground than that. I think
all of on foot combat is pants,
not just the sniper rifle bit.

But, a slow moving projectile is already at a disadvantage (i.e. vs a moving/patrolling target) at a distance. Unless you meta the hit animation to send a follow up shot instantly, all you've really done is dropped their shields, put them on alert, and sent them running for cover for a shield recharge. But, if Shurimal is right and a body shot can take them down just the same, then you just need to know what area of CM is constant during a hit animation and can double tap that. It's still meta, though.
I wonder if their shields ever run out of battery? Do they ever drop them once their alertness normalizes? Can you wait them out and take them in a single shot? I doubt all of this. My money is on mobs being coded with infinite shield batteries/ammo/etc. when they have been alerted to make up for the fact that they don't have brains and we do.
But, I'm going to experiment a little more with stealth and the plasma rifle. To be fair, I found the whole on foot affair to play like a pre-alpha release and generally stopped bothering with on foot combat for the sake of gaming fun, so I haven't explored every nook and cranny of the experience. But, now I'm academically curious...
To be clear, though. I'm not expecting Call of Duty. I'm not really expecting anything, honestly. I would have preferred if the DLC refined and added depth to what was already there with the space flight aspect rather than expand their breadth with a poorly optimized basic FPS element that's in the neighborhood of a second-rate arcade shooter (and adding more ships when inventory is already redundant is really not necessary). Especially when you contrast the two sides of it, the flaws of On Foot are even more apparent. In my opinion, the counter argument here is basically "On Foot wasn't meant to be that great" but is it a counter argument when people are essentially saying "On Foot isn't that great"? Like, we're arguing and agreeing at the same time.