I'm not going to claim to be a shooting expert but I do like to think I'm half-way decent at shooting things in games at this point by the amount of video games I play, and how many of them I play on the hardest difficulty possible when playing, many of them featuring shooting. Also as a person who's played Resident Evil 4, 5, & 6 a stupid amount of times as I've had way too many friends ask to play those with me (not that I mind, but my RE5 playtime in particular is fucking ridiculous, so many of my friends had it and so many asked me to play with them their first time through the game, or play Mercenaries, or the DLC, or whatever, my total playtime between the 360 and PC version of the game is almost 600 hours, and that's between over 20 playthroughs of the game and a lot of Mercenaries and DLC playing, I have a large group of friends I play games with).
Sorry, got a bit off topic there, was just remembering that and rambling. Anyways, the shooting is actually a bit difficult, you do get better at it with some practice, but it's harder than your typical game with shooting in it for a few elements.
00.) This is just a bonus comment before I start talking about this, but the footage you may have seen may be on Casual Difficulty. I believe there's some aim assist on Casual Difficulty.
01.) This first element some may view as superficial difficulty but I think it makes sense to the gameplay and the fact this isn't an action game. Sebastian's aim is not perfect to the players. Now, this element can be upgraded with green gel and I assume if you maxed it out it'd basically control his shooting like any other shooter where he shoots where you point the reticle,
I believe in any image where you see a reticle like this, the player is fully upgraded on their steadiness trait with green gel. THE REASON, is because I know for a fact when I played the demo there was a big box around my reticle, at first I didn't know why, but I figured out it's because that box represented the AREA Sebastian might shoot when I took a shot. It was basically a display of his 'area he might shoot when you take a shot'. The box changed between the Handgun and the Shotgun, with the Shotgun area being much wider than the Handgun's. However, when I upgraded by steadiness trait, I noticed the box got smaller. So I assume since in videos like these there's no box when they have the reticle UI turned on, they have the stat maxed out. The same thing applies to videos where I see Sebastian run for more than 5-8 seconds, since in the demo he can only run that long before tiring out on level 1, thought upgrading it to level 2 increased it to 12-16 seconds.
So especially at first it may be difficult because on lower aiming levels, Sebastian doesn't always shoot in the middle with the point, he shoots in this boxed area. It gets effected by a few traits like distance, if you're moving your character or the gun around a lot, etc., so not truly random, but Sebastian's accuracy is not that of the players fully on lower levels because his aim isn't always dead-on to where the player is looking, at least on lower levels again. That was one element that made it a lot harder, but didn't feel unfair either again because the game defined how it worked and the focus isn't on killing every enemy anyway. There wasn't enough ammo in any of my runs to kill all the enemies in the mansion, and shooting is presented to be a helpful but unreliable for every scenario thing.
02.) Shooting them anywhere in the head doesn't cut it. They will loose chunks of their face and skull often when shooting them there, in big part because this game has a lot smaller hit boxes than it does in other games of its kind. I don't think this will be fully understood until people play the game, but the enemies have much smaller weak areas to shoot to get them to react. Visually on the head the parts of the fact being shot off is a nice touch, but you need to sort of shoot a very small dead point to take out the enemies.
03.) And this next element applies to the above too, on-top of this, the enemies bob and move around a lot. They often don't come at you in a straight line, they'll bob and weave around. Some will run at you with a dagger while strafing left and right. Some will see you trying to aim on their heads and while they dash at you duck their heads and upper halves of their bodies down while lunging at you. And they move very unnaturally as it is, sometimes they'll begin shaking their heads almost Jacob's Ladder style (not nearly as fast, but same sort of thing), or suddenly just start bobbing their bodies around and moving it unnaturally. It makes them a lot harder to shoot.
04.) To all of this, one more thing that can be upgraded, or two more things really but they're related. Sebastian has a shakiness to his aim naturally, especially on level 1 when you're just taking aim. And he also has recoil, so after you take a shot, your gun moves from position from where you were aiming so you can't just take rapid shots. Both of these elements can be upgraded with green gel, though.
I am guessing that achievement for beating the game without upgrading anything will be fun.