Display connectors ever so slightly damaged - cause of broken display?

Bought a damaged iPhone off of someone who *claimed* to of dropped it and the screen to stop working.

I took the iPhone apart to find the battery all wrinkled up as if it's been soaked in water and it was very flimsy to the point where I would be been able to snap it in half effortlessly. I replaced the battery, and now this part is working. I identified this by plugging the iPhone into my Mac which opened up iTunes and Photos.

So my Mac can see the iPhone perfectly fine, comes up in Photos displaying the photos on the iPhone, but there aren't any to display anyway. Comes up in iTunes asking if I want to allow this computer to access information on this IPhone. I select continue and it prompts me to accept on the iPhone screen, obviously the screen isn't working so I can't get any further at this point.

I tried the screen it came with, with the new battery but no luck. I don't currently have a replacement screen to try, but I did have a look at the connectors under a magnifying glass on the existing display assembly (bar the camera, sensor and home button). I noticed the odd one or two damaged pins; perhaps more couldn't tell for sure with this strength of magnification. Now, working in PC repair where things are bigger and less delicate, such little damage to the connectors makes me think it's not that. But my question is how damaged do they need to be to cause the screen to not function?

It should also be noted that a few brackets and almost all screws are missing, so components like the lighting connector, speaker and headphone jack are all loose. Although because I can get the iPhone to,come up in iTunes I don't think it matters too much.