Is this true? Am I missing something?
As always, to accurately answer your question, you would need to benchmark your specific circumstances and workload.
Personally I use Debian Bookworm as my desktop. But prefer to use Alpine Linux for servers with external access. I have tried various BSDs, but I find the cognitive load of remembering two different ways of doing many sysadmin tasks an unnecessary burden.
Yeah, I might just have to spin up a couple of $4 DigitalOcean servers and profile them against an actual running e.g. PHP web app, file server, Django app, etc.
The fact that there doesn't seem to be an overwhelming "Of course X is better than Y" consensus suggests that the differences are within an OOM of each other in nonspecialist cases, though.
Also, I feel like FreeBSD will eventually enter the "immutable server distro" space. ZFS boot environments have had 1st class support for over a decade already. New container advancements are being made on FreeBSD every year. I really believe it could compete hard with Fedora Atomic and OpenSuse MicroOS.
If using it, did you tune it, or the Linuxen, or let them be at their defaults, more or less?
How do you expect/want to use it?
Would 'less churn' be of value to you?
I am most interested in the out of the box experience. If we're going to compare tuning for maximum performance, we probably need someone who has experience tuning both kinds of boxes for that, to get a minimally biased read.
"Less churn" is always a valuable property, and one the BSDs are famous for, but at least personally I experience manageably little churn on Debian servers as-is. Churn and its consequences seems to come down more to personal familiarity than anything, and so I don't really include it under the banner of technical reasons per se.