So I finally have the desired Fediverse setup. Here's the changes that I did:
- moved Friendica from social.plantroon.com to plantroon.com
- restored all the posts I could from social.plantroon.com that ran on Pleroma
- imported contacts
- recompressed photos from my feed
- on matrix side, I cancelled any reference to matrix.plantroon.com domain

The best thing is that I can still have my blog at plantroon.com. So no losses at all. One of possible scenarios was moving the blog to blog.plantroon.com subdomain while having Friendica at the root domain.