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Maybe I saw increases for a few months because it took some time for the increase in the home page’s word count to be assessed by Google on a site level, and then compared to the “norm” in the niche?
If a page on my site had less content than the homepage then it makes sense that the page does not have enough oomph to be considered a quality page.
I would think about going back through the 25% of pages and seeing if you can improve them in any way.
You don't want your home page to be providing more detail about a product, service, or subject than your inner pages do.
For example, a website about Subject A should have more than 10,000 words?