Thanks for these insights! I guess I’ll do the same and put Lightburn on my old laptop and run it directly. Honestly, my hopes are not too high: Often the touchscreen controller already shows 100% while the device is still executing several moves - which I assume is an indication that the touchscreen also uses buffered commands.
In the meantime I have continued my experiments, and I am considerably frustrated and thrilled at the same time. I am thrilled because the 2W tiny focus allows for such a detail, and also that true greyscale in principle works, but frustrated because the stupid software gets once again in the way.
I lowered the laser movement speed, down to 2000 mm/min in the end, but the laser still moves visibly slower in dotted regions than if it can do a longer stretch. So it is not only the absolute speed that causes the problem - even at moderate speeds the effect of command processing is there and creates problems. Here are a few results - I plan to laser Escher’s metamorphosis strip and picked a few very different parts as test patches. The top, “complete” image is done with dithering, not greyscale, and even that is not too shabby. The lower, incomplete image is the same as true greyscale.
The arrow points on a square which is full white - and because of that, Lightburn cleverly says: Let’s not split this into single dots, but let the laser run a few mm at max assigned power - just one GCode command for a few mm’s rather than dozens in the more dynamic regions. The result is that the laser can finally speed up, and the laser energy disposed is no longer good enough to get the square fully white - so instead of being the brightest part of the image, it is slightly darker than the surroundings. And you can even see the speed-up and slow-down phase of the laser - so trapezoid power adjustment not up to the situation or not working at all 
And as you can see, the problem is true either for dither and for greyscale…
Oh, btw - the height of the full image is 33 mm - this gives you an idea of the stunning detail you get with the 2W!
But where I have the slowed-down dots, greyscale is really nice - here’s a detail for comparison - top dithered, bottom greyscale, the lower strip is 6mm high (these details!!!):
This gives me hope - I’ll get there eventually…