I have written right at the beginning, why not using extensions removes essential capabilities out

Nope. I disagree with that premise. I do not need anything an extension can provide (in the use case of 90% random browsing), and all extensions are a security risk. I would prefer to have an extension free, adblock built in, cookie tossing on close by default, simple browser as my go to for most everything I would use a browser on mobile for.

Now for that other 10% of browsing, maybe I would like a secure, blob free, hardened browser. But that is not the use case I was talking about Focus for.