Hello!
As someone who is bothered by small differences in style, I recommend switching out the many out of style (in Hoenn's case) and the many mismatched (in Kanto's case) overworld sprites with sprites more along the lines of the Diamond and Pearl style, along with sprites more aligned with the trainer sprites. Understandably it's a lot of work, but I'd be more than happy to help out. I did up a handful of the worst offenders. Some are mere edits, and a good few are complete redos. https://imgur.com/a/8IvOykc