Which are, respectively, based on 4.9 and 4.11 in ports. The AMD has made large strides since then. In those kernels, the amdgpu driver barely supported Southern/Sea Islands. These work extremely well with recent kernels (much smoother than the old radeon driver). Vega cards only support graphical output since 4.15.
Wayland is enabled by default since recently.
The FreeBSD website states that Wayland is not ready for general use. Wayland has been 'enabled' in many Linux distributions for years, but it took a long time to remove all the wrinkles.
I wonder: did you actually run a full GNOME desktop on Wayland on FreeBSD for a couple of months?
Linux - Vulnerabilities (2103) - FreeBSD - Vulnerabilities (368)
Linux is far more popular and most likely audited more as a result of that. So, it is not surprising that it has more CVEs. Also, the Linux kernel is a fair bit larger, supports more architecture, and more hardware, which means more surface.
About 7 times more on the Linux side, do not mix X11 into that :)
X11 is a permanent security vulnerability. Every application can read each other application's mouse events, key strokes, and do screen grabs.