Why not just say it?
"Sadly the graphics support is still lacking on FreeBSD since all the driver development is very linux specific, we therefore decided to switch kernels because graphics is a major part of the user experience."
The FreeBSD wireless driver space is also pretty dated. Only 802.11N is supported -- the one or two 802.11AC WNICs that have support just run in the slower N mode.
In short, the situation is getting better and isn't awful (especially on nvidia graphics and wired NIC hardware), but the concerns TrueOS has are totally valid and won't be completely eliminated even if FreeBSD stays caught up in the graphics space.
Having said that, if they use the same frameworks as the x86 drivers, the work on Intel and AMD ports should make porting them easier as well, since it all revolves around linuxkpi - shims that provide Linux-compatible API for kernel code.
Not only that, there's often some kind of dependency between GPU/display HW and platform clocks/IOMMU/etc blocks that we might have completely different drivers for. This embedded crap is super messy, why can't everyone use PCI for everything inside the SoC >_<