Deindexing old site. Using Same content in new site. Possible?

I have a 3 year old website with content is high quality and 200 article of 1000 words each and I dont want this content to go to waste.

I could never maintain a proper linkvelocity for this website. For past 3 years, I post some PBN links then forget for next 6 months. And now when I am totally focused on this site now, it is not moving up may be because of irregular link building record.

Most KWs are stuck on page 2 and 3 for past 20 months. Should I deindex this website and redirect it to new site with old content?