Things I tried are mainly:
- Different amount of CPUs (not 1 though), memory, video memory - no noticable differences
- Scale factors, both, via the guest OS, and via vbox - I believe the latter has a small effect, but maybe that's imagination
- Graphics Controllers - for me this has the biggest effect, with VMSVGA being a bit faster, but I believe that the reason for this at least partly is connected to me not being able to use fullscreen (with guest additions installed - I even did a whole installation with VMSVGA to rule out any problems which might stem from switching the controller). For the Parrot installation VMSVGA also broke some fonts, or so in Parrot, where the menu texts of the OS were not shown anymore (this only happened for Parrot - more than once, although it still could be my fault, I didn't try to fix it, because it didn't really solve the slowishness, either).
I'd be willing to play around a bit, if I have time, but I'm in no way an macOS expert. I read something about pointing devices programs, which could cause the problem in one of the links socratis posted - maybe I'll find something. If someone has more concrete suggestions... For me, moving the vbox window to another monitor didn't change anything about the performance. But in my case the external monitor is a highDPI-monitor, too.
I'll add one logfile, just in case I'm having an obvious error in my configuration.