Extra problem: 2.0.760 (Windows) is my launcher version, Affects Version has not allowed that. (it is the surprise)
Old launcher: no problems, fast, I can copy text and all I need (which could have been written hours in the past).
New launcher: no game output after a few minutes and while starting. At first it was minutes behind and then the window turned entirely white, except the headline. So I cannot copy chat in multiplayer. At 100 lines the delay is already getting unbearable sometimes, several seconds.
So the problem is, that the new design takes far too much of my performance (which is ingame not that bad, up to my 30fps-limit). If some mod wants to tell me go to technical support: No, it was good, it is now bad, something that worked, does not now, typical for bugs. And I know: /r/minecraftsuggestions, the old style caused no problems, give it an option.