Thanks for the reply!
I am absolutely amazed that the "only" sollution for this most fundamental function is a 300 euro plug-in. That's... very sad for a software as user-friendly as SketchUp.
Well, I guess it will be wiser to man up and switch to Blender after all and get all I need for free.
But still! Thank you for information. 
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The Question / TL;DR on the bottom!
I've been working with Sketchup even before I went into game industry, so it was an obvious choice for my 3D modelling software. But lately, I've ran into a problem, which cripples SketchUp beyond usability in any intermediate game making process.
The problem is optimalisation versus workflow.
While creating a complex 3D model with many curved surfaces (f.e. a cathedral with arched windows all over the place), I use the UV Toolkit to make texturing a lightning-fast, nearly one-click process (saving time, which I can then use to make more models, sounds, programming and so on; great workflow).
BUT! It generates a separate material and texture to every quad face. When a model has 6459 quad faces (and it's not even it's final form!), it makes a ridiculous amount of unnecessary materials, which then have to be rendered by the game engine in every frame (here: Unity), slaughtering performance, it's family and it's dog with it. Of course, I could assign all the textures by hand, using build-in texute positioning Pins, but spending additional 100 hours~ on every bigger asset is not really an option.
THE QUESTION / TL;DR / CONCLUSION
Is there a swift way to generate a texture Atlas (closing all textures in one "big texture" and one material) inside SketchUp, or should I consider it obsolete in gaming industry and switch to Blender or 3DS (which I'm not very happy about)?