I think most of you will find that the problem is more about inputs than timing. Go in that lab and just try to mash 1+2+3+4. The button prompts will show up on the edge of the screen as: 1+3, and then a line below it: 2+4
or 1+2+3, and below that, 4. So my problem is actually hitting all 4 inputs in such a way that the game considers it simultaneous.
I will also add that Switch Stance + Interactable doesn't work in any form of combo from my experience. The game actually considers these different button inputs. That might be confusing because they happen to perform the same function as e.g. 3+4. The final slam can only be done by actually hitting 1+2+3+4 as far as I can tell.
I'm using the Dualshock 4 and one way I've found is to just put my thumb right in the center of the face buttons, so that it's like half-way on each of them, and mash hard and fast. The other way is to lay your index finger across 1 and 3 and your middle finger across 2 and 4. If you try that, you probably just need to practice it for the whole sequence so you aren't scrambling to get your fingers positioned right. Not enough time for that.
