If you are a native English speaker and have a true passion for your niche and have a deep understanding of it, you shouldn't need to rewrite anything but rather be able to come up with your own unique content from multiple primary sources. For example, by referring to scientific studies or peer reviewed journals and then taking what you learned and putting it into a way your readers can understand and resonate with. Most people, even if they are native English speakers, can't read and understand complex texts. If you have a high level of education and are really interested in your niche I think that's the best way to create unique and original content. Once you have that in depth knowledge you can add to it with your own unique ideas too.
If you want to build a site to make some ad revenue rehashing old content is the way to go. If you want to build a business and a brand (including a brand that includes you) then I think you need to be truly passionate about your niche and be able to bring some original thinking to it. One example from youtube is Linus Tech Tips (not affiliated with him in any way). He has a channel where he talks about computer hardware of all things. It's unbelievably saturated. He has over 9 million subs though since he has original content in this niche that actually solves problems the content consumers have.