Maybe in your book.
In https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard, /usr is the common directory to install programs and libraries, for read-only user data.
Same book, other operating system and what about Lazarus ? Do you install that there too ?
It is inconsistent to say the least not to mention that on Linux you do not always have the luxury to have write access to /usr
But yes, maybe for trunk it is not the best choice.
Since things are inconsistent amongst platforms and programs you have to be a bit more inventive and not let yourself be boxed in with some imaginary rules that seems to exist with the purpose of pestering developers/people.
It is a bad idea to use /usr for moving targets such as trunk.
As a consequence and (for me) to be consistent all my FPC and Lazarus installations are completely stand-alone and do not rely on anything other then 2 environment variables and a script. No paths, system directories, OS deemed correct location(s) or otherwise is required.
The FPC developers did such a good job of getting rid of all such dependencies that it is almost unbearable to see people struggle with installing in program files, requiring sudo rights to be able to install their fresh compiler and/or run Lazarus etc. The only thing I used to recommend is for users that are new to FPC / Lazarus is to use their package manager to install but, some distributions made such a mess of things that I can't even recommend that anymore (and people requiring multiple installations should really stay away from using a package manager unless they can bent it to their will).
Completely off-topic of course, therefor apologies to topic starter. There is no intention to derail the thread.