That`s totally it!!!
I said this in the production forum, 90% of good production IS choosing the correct sounds to fill the space you want them to fill.
Rather than just choosing whatever you want and then trying to hammer it into the mix, each time you add a new sound, think about what frequencies in the mix are full, and which are empty, and find sounds that will fit into that space without too much surgery.
It should be a very natural part of composition.
It seems you certainly are on the path of the Jedi master.
It`s a very long one, and I`m not sure it actually ends!!!