Yocto is synonymous with low-end IoT these days, and causes more problems than it solves in the long-term for many folks.

Also, bootstrapping your own application launcher shell on a raw kernel is usually not a difficult task (depending on vendor firmware.) Some folks just drop a full Lua environment for an OS that fits in under 2.7MB ISO even with a modern kernel.

Nir Lichtman posted a tutorial for mere mortals here:

https://www.youtube.com/watch?v=u2Juz5sQyYQ

Highly recommended exercise for students =3

I think that's fair, but it does depend on what you want the relationship with your SoC vendor and the Yocto community to be. A lot of SoCs have pretty good community support in Yocto (and probably Buildroot), and using a community-maintained BSP meta layer will make things easier for you in some ways. SoC vendors aren't always great at following Yocto best practices. Plus, unless you have excellent support contracts with your vendor and are prepared to use it, you'll probably go to the Yocto community for support with weird Yocto issues you run into; and Yocto developers are (understandably) much more helpful if you say you use mainline Linux with a BSP maintained by the Yocto project than if you use a vendor's kernel fork with a BSP maintained by the SoC vendor.

Buildroot is easy to use even without vendor support