After some more troubleshooting I found the real issue. What I did to arrive to that conclusion :
- I waited until I couldn't anymore and decide that I was gonna pay the shop the 25€ to test the GPU and just before going out I decided to search the web for something I didn't tried yet.
- After thinking about any and everything I could for an hour or two, I search for DisplayPort issue reports and found a ton of people reporting the same problem. One solution, in particular, was acknowledged to work so I said to myself I've got nothing to lose and tried it before going out. And as dumb as this solution sounds it worked! The solution was to turn off the computer and unplug the display from everything(from power source and PC) and let it sit for 60 seconds or more and then plug everything back up again and start the computer. My rig worked like a charm for 4-5 hours straight, I was so astonished I almost cried and wanted to throw the PC out the window or for it to be human so it can get cancer and feel as bad as I felt for 2 weeks+. I ran Heaven\Valley benchs on extreme settings for the entire time to be sure the GPU wasn't faulty while taking a nap. I woke up and it was still running no problem. I was so happy. Then I started to watch a stream while surfing on tech sites preparing myself to close this thread and the problem came back out of nowhere...just like this. I wasn't even mad nor sad, lol, because I was relieved that my GPU wasn't faulty. I turned the PC off, removed the GPU and went back to the iGPU instead. Everything was working but I noticed that the wiggling the DP cable was making the screen go black...and started remembering the numerous occasions my screen went black for no reason at all...but moving the mouse seemed to brush the problem away so I didn't figure.
One thing I noticed in the OSD of the display was weird settings when the GPU was plugged in for example : 0hz instead of 144hz and other stuff(thought it was a firmware issue but it wasn't). But the OSD was ok when using the iGPU displaying everything fine. I just had found the culprit! (I can't, for the life of me, explain why the cable worked when using the iGPU from the motherboard DP and not with my GTX1070...maybe power requirements Idk?????)
To be sure of that and that my GPU and display ports weren't fried, the next day I went and bought a HDMI cable(waiting for the new DisplayPort cable I ordered off Amazon to arrive a few days later) in an electronics shop near my house and tried it with the GPU and it worked right away flawlessly for the rest of the day(but at 60hz because HDMI 2.0 can't manage 144hz) so I was sure that I had found the real problem.
By the grace of the shaman disciple that I wish to be, my new DP cable arrive 2 days earlier and by that I mean in the evening of the events so I swapped it with the HDMI cable and it's been working flawlessly since. I even played games and kept the rig running all night until now with no issue whatsoever. I'm so relieved.
- About the DisplayPort cable : while searching for reports on it, I stumbled on a Geforce forum post that talked about the original DP cable coming with his display killing 2 GPUs of his and the troubleshooting he has done so far and other diverse forum posts about certified VESA DisplayPort cables and other stuff. I search for a certified DP cable brand on a website referencing them by models and serial numbers, found one really well reviewed off Amazon for 28€, bought it and it is perfect. The original DP that came with my display is in the trashbin. Really bad quality.