I have never seen anyone do this type of shimming or spacers before. There is a old (15 yr old house) settlement crack above a door in the master bedroom that I think was caused by this shim being placed vertical and not laying flat.
Whatever the cause, what your pictures show is a really bad idea. Wood shims/spacers - bad. 2x4’s on edge - even worse. You can see in the first picture where they are starting to distort. Only a matter of time before the grain separates and they fail completely.
4" space or more requires masonry, I believe.