Not everybody has a third hand. :) All kidding aside, they recycle a lot of steps from other fixes, you can see if you look at other guides for the iPhone. It was probably just easy for them to tell us to remove everything rather than explain how to hold the screen at 90° while working on all the other delicate steps. You are right though, there's no need to disconnect and then do the tricky reconnections, which probably account for most of the complaints you see here.
Everything went well, except it took 2 people and 1 hour, much harder than other ifixit "moderate" tasks that I've done before. Everything worked great, the "new" battery was 1.5 years old, but unlike some cheap alternatives, at least had all serial #s and dates. I'm back to having 24 hours of moderate use per charge.
Everybody needs to understand that these fixes are intended for people who really enjoy hacking around. There is serious risk of damaging your phone, you have to accept that before you start! We followed a user tip to have a white cloth to hold all parts, just lay them from top to bottom in order. Also, we used tweezers to manipulate the small screws that were not magnetic. We accidentally disconnected a small cable right next to the battery cable, but it popped right back in. All cable connections were challenging to fit back in, just need to wiggle gently until you hear the click. Having that extra hand is very helpful to hold the screen assembly, whether you choose to disconnect it or not.
Sounds like during the unexpected release of the screen, maybe you accidentally damaged or disconnected the LED light guides that spread the light over the screen? The light is stuck at the top, making hot spots.
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