Those numbers look pretty normal, and from the output of that network graph, it’s pretty clear the actual problem is that your CPU isn’t keeping up with the game, unfortunately. That’s expected behavior on this machine, and the FPS numbers you’re seeing there are pretty much expected. I’m going to have to reiterate my earlier information in this case, given all the tests you’ve just done. Since the CPU isn’t overheating, and we can see those lines go crazy when the CPU slows down, and since the problem improves when the CPU is being less utilized, you’ll need a PC tech to physically test your hardware, or a new computer to improve the performance.
If you want to try avoiding that for a little longer, the last thing I’d have you try is checking out WyomingMist’s guide on overwatch performance. They bring up a lot of great pro tips for optimizing performance even on minimum spec machines like this.