I really don't think they did all that bad.
As noted, a car doesn't do all that much to stop rifle bullets. If the healthy officer gets in a car goes 20 yards up the road, stops, lets the hit officer jump in then backs up, you are talking about a lot of exposure to both of them. If the guy who is hit can get out of the line of fire himself, then the healthy officer covering him while he does so makes sense.
I am not sure when the other officers down the road arrive. The footage does not initially show them or the spot they are later seen at. They have a lot more firepower than the officer close to the videographer. Until they show up the healthy officer must pay attention to the shooters location. Afterwards, from what the video shows, he is still holding the weakest point of the box, so if the shooter makes a run for it he likely will come right at them(and be full of holes before he gets there). Maybe shooter is in a house and will drop out a window the officers down the street can't see. All the same he needs to keep an eye on that situation.
Ever shot with blood all over your hands? I haven't, but even in the rain controlling the firearm is considerably more difficult. I do know blood is considerably more slippery than water. I wouldn't want blood on my hands in a shoot out if it could be avoided.
The civilian leaning against the car who helped pull the officer across the road is clearly having problems with the situation. Not sure he will be able to help much. I was in some medical training where we responded to a simulated scenario with a person unconscious and had to figure out what was going on. My partner went to check pulse and the hand came out of the sleeve. Fake hand, the actor made a pretty realistic unconsiouc groaning reaction, and my partner THREW the hand over her shoulder and fell back. It was several minutes later before she was functioning. Blood isn't for everyone.
The videographer is some sort of media person whether freelance, amateur, or professional. Media makes a choice on whether to observe or participate. If they decide to participate they won't make a living observing and we won't have a record of events.
Applying pressure through kevlar is not all that easy. Looks as if the hit is at the edge or just under it(likely folding). Still difficult to work around it. Taking off the vest isn't a great idea either.
You can apply pressure and retain some view of the shooters location. Lay prone and use the other officers body as a rest. Finding a position where you put enough pressure on the wound without putting pressure on the lungs and still remain able to shoot would be a challenge. Not a great solution, but if you have to get both jobs done...