The changes are probably as not as radical as they might first appear. If there is one problem I've always had with F-Secure is its deliberate unwillingness to be forthright (transparent) about product details. The staff are instructed to say nothing or virtually nothing as if they hold the world's nuclear missile launch codes.
It is so dumb. Ridiculous. Now, F-Secure no longer hides that it is using Avira components. There is no problem with Avira signatures, but if integrating those components reduces or eliminates useful product features (such as detailed error messages in scan logs) or negatively impacts protections, then there is a real problem. Avira is not so great at handling exploits. Not that F-Secure has ever shown that its own technology was very good at handling exploits either.
All said, at the end of the day, F-Secure remains one of the better options for the security illiterate and dis-inclined. That is until banking protection blocks one of them doing financial online transactions and they don't know how to handle it. They just turn off banking protection, which is one of the main reasons to use F-Secure.
Native Windows security is the best bang for the buck, but I lament that it is a societal guffaw - Windows native security is far too much a jigsaw puzzle of patchworked features, configurations, and exceptions to those configurations. Then there are all the unexpected behaviors which are expected but Microsoft never tells anyone they are expected.
@Andy Ful is the SME on that. His long threads are the proof of my statement.
SpyNetGirl's Github page is proof that Windows native security is intended for enterprise. Not consumers. By extension, Windows is intended and designed for enterprise. Not consumers. This statement of fact is irrefutable. And so it goes in the world of digital security.