I see basic one page websites doing well in organic results. How do you think they get away with this?

If you wish several applicable contents for you, it would be wise on your part to get near 6-12 decent content pages on several topics or pages answering related questions to your niche.

I also think there is no need to upload new content in website you can do via off page work for promoting the website.

Content is king in seo...

New content is SEO will continuously place your content before search engines and will distract the attention of the readers. It will ensure the viewers that you are ready with customer support and answers of customer queries every time they ask.

Yeah ofcourse fresh content speaks 100% true factors and boost rankings to the site too....

I task myself with making itty bitty tweaks to each and every piece of content on my site at least once a month. I guess the search engines see it as fresh content?

If not, I'm still good as I add at least 5-10 articles every month (that I write myself for the sake of quality). I'm reaping the benefits of my efforts.

Yes Website need fresh content for seo because of google penalized by duplicate content