80A is a serious amount of current, and if you combine that with thin copper, you may get into problems with localized (over) heating near connectors.
At the moment it looks like you're injecting 80A into a corner of the PCB, and then transport (a part of it) to the other extreme end. Compare that with putting the 80A connector in the middle (halves the distance) and you have 40A going up and 40A going down. On top of that, you have better heat spreading around the high current connector.
Have you thought about making a dual PCB project?
For example, Use one PCB with thick copper for Power distribution and some MOSfets, and another PCB for small stuff such as a microcontroller, and then combine them with either a connector or use castellated edges for the digital PCB.
Maybe you can even keep both dual-layered, but even if you want to keep the "microcontroller" PCB as 4-layers, it's likely a much smaller PCB.