Grayscale with diode lasers is much easier than with CO2. If that was your first grayscale result, you might have a settings issue. Starting with a color or black and white photo, you should be able to do things like this:
That image was done with a 4.5w diode laser, using no external image processing - I just dropped the image into LightBurn, entered the settings, made some adjustments to contrast and brightness, and burned it.
Full settings are shown with the original post here: