Indeed, each system bears its distinctive advantages and drawbacks, and the optimal choice often hinges on the specific requirements of the task at hand. Nonetheless, I believe that OpenBSD's utility is limited in contemporary scenarios.
Culture
It's undeniable that OpenBSD has spawned important technologies under its "shut up and hack" mantra, cultivating an environment conducive to technical breakthroughs. Conversely, the Linux ecosystem too has been a breeding ground for major projects, Docker and Git being just a couple of examples. The ethos within each community can differ considerably, contingent upon the project or distribution. The widespread popularity of Linux may attract a varied spectrum of users, some less technically adept than the typical OpenBSD user. However, that doesn't mean it's short on technologically adept contributors.
Predictability
I've chosen to make peace with systemd, seeing it as a necessary compromise, as it has become the preferred choice amongst the developer community. Unless one fancies rewriting systemd .unit files each time something needs to be installed (which I don't), the practical choice is to work with it.
Concerning the upgrading process, many Linux distributions today offer smooth upgrades without necessitating a complete reinstall. Your encounter may rely on the particular distribution you're using. Perhaps it's been a while since you last used Linux. I haven't come across a distro that requires a complete overhaul in quite some time. Rolling release distros are now increasingly prevalent and are even suggested for novices.
With nixos, which is my distribution of choice for the foreseeable future, I have an attribute that your OpenBSD system lacks: reproducibility. I can transfer a handful of configuration files to a brand new computer and replicate my system precisely, encompassing all my installed packages and configurations, including those in $XDG_CONFIG_HOME. It will literally recreate the same exact environment.
History
And both of them are inspired by Unix, what's your point? :P
Why should a company that needs to make money selling software be “antiquated” simply because (for example) some of its algorithms are trade secrets?
I think we're not gonna agree on this, but I believe that all code that matters should be FOSS, there is no reason for a company to keep their algorithms as trade secrets, and if anything being open source can only improve the world, not hinder it.