No, it's not. You can go from one GNU/Linux distro to another GNU/Linux distro and you're still gonna find a GNU userland and a Linux kernel. Base userland and kernel differ significantly between BSDs.
plus - native binaries can be copied between one and the other and run natively without any emulation layer provided the c library, kernel version, and other libraries are reasonably similar.
> If you use Linux with systemd or without is a significant difference, which is probably as big as switching between BSDs.
I did address the init daemon point. With Linux distros you're still using a common kernel upstream (ie Linux) which all Linux distro's share. That's not the case with the BSDs. You're also sharing the same GNU coreutils which 99% of Linux's share, BSD's often have their own. The kernel is really the key point here though.
> The name of my operating system is "Ubuntu", not "Linux".
Technically it's neither. "Ubuntu" is the distribution name. "Linux" is the kernel name. I don't much agree with Richard Stallman that "Linux the OS" should be named "GNU/Linux" but from a technical standpoint it is a more accurate OS name than either of the two suggestions you raised.
No, it's not. You can go from one GNU/Linux distro to another GNU/Linux distro and you're still gonna find a GNU userland and a Linux kernel. Base userland and kernel differ significantly between BSDs.