What is the importance of onpage and offpage optimization recently? one of my webpages is gradually decreased from page 1 to now page 2 SERP position 16 in last 3 months . I think It will go on to 3rd page and further down.

Till 3 months back, the content was good for google to put it in the first page SERP 8 or 9. The content is 100% original and is meant to sell a product through affiliate network. There are no updates to that page. But there were no updates 3 months back as well.

Recently google shows different pages of a product from the same seller (like Amazon) in front of my page and naturally my page will go down because of that. Those pages are from a site which are having a good PR, but they dont have much content and are pages enlisting their product.