driven by developers working at red hat, who has their business customers in mind when they make big changes like introducing systemd.

Systemd isn’t a kernel change. It’s generally adopted by most distros, but since it isn’t actually in Linux, you don’t have to use it at all and there are plenty of alternatives. There are even distros dedicated to using alternatives for systemd. I’d take a look at Artix, Devuan, Void Linux, and GNU Guix.

The linux kernel is itself open source, but that can’t stop people from building something proprietary on top of it

The GPL will force all changes to be released under the same open source license.