I disagree with Kliment about only 1% of Sketch being usable. Perhaps many of the pre-defined settings don't give pleasant results, but they are just examples. You have control of most of the effects via the sliders.
In your first example, you had the 'air' perspective effect too high, which causes linework to fade out (I think).
In your example with a dark background, you needed to change your sketch lines to a light color to make them contrast for visibility.
The sketch render is always transparent, so you cannot put a 'sky' behind it, for example. But, you will find other threads here where people have done clever things, such as making a LightWorks or Internal render, saving that as the sketch background image, and then generating a sketch which in effect places sketch lines on top of the render. Other effects require an image editor such as Photoshop, Gimp, etc.
Like any creative tool, it takes time to explore and find what meets your needs.
Cheers,
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB