> required many years until achieving a decent implementation for multi-threaded CPUs and during that time they have remained long behind Linux and other operating systems

Many OSes at the time had hitches with SMP. BSD was one of them. FreeBSD had SMP in 4.x but almost everything in the kernel was single-threaded and the kernel thread was a major bottleneck.

FreeBSD wasn't alone in this. Linux suffered from a similar problem at the time, also because of the driver architecture. (The infamous "big kernel lock" wasn't fully eliminated until 2011: https://kernelnewbies.org/BigKernelLock)

This is an area where NT was much better, or VMS, or Solaris. And yes, the SMP issue, in hindsight, does partly explain why both Linux and BSD weren't as historically attractive as they otherwise looked, for large systems.