I'm not watching that video, but, I'll say this, the dude is level 46!
I'm playing my third playthrough on very hard and it is indeed very hard. By the time I can mass kill everyone with that contagion cyberware I will have earned it, and will bloody well enjoy it.
As others have mentioned you don't have to be that level to do this.
And I don't disagree with you, that you should feel stronger as you improve your character and become more badass. But in my opinion this has nothing to do with that. This is simply like playing with wallhack and the enemies just standing there unable to do anything, whether that is sniping or hacking them through the walls or headshotting them with a pistol, if its a normal pistol fair enough, because you actually need to be in line of sight with your target.
But these things renders cover and using tactic completely obsolete because you don't need it, if you can just kill them as if there were no walls.
And yes it's fun the first 5-10 times you clear enemies like this, but after that it just becomes silly and boring, and if you haven't reach that state in the game yet, I would suggest going all nuts and see if you can keep up the excitement for very long when it comes to combat.
To me it ruins the whole mechanic to just kill everything through walls, because it doesn't matter how much armor or whatever you have, as it's really easy to spot enemies with ping or through cameras or just stealth around and it takes them a long time, even if they spot you, before they actually agro you, so you can in most cases just go behind the corner or whatever and they lose interest in you.
So when you reach that state in the game, I would really like to hear if you after having done it 30+ times, still have the same excitement for it.
If you worry about his build being OPed or spoilery. Its not, I arrived at the exact same one as well and my guess is that most will, because it's in no way a special thing. It's just how weapons and hacking works in CP.