Loading Plots takes 13 seconds for me. Seems non-negligble.
It is relevant because in the issue I linked none of the Requires enabled packages are loaded but Requires still causes extra compile time (you need to compile all the Requires expressions).
As already explained, Requires causes extra load time anyway. Also, one of the main “features” of Plots is presumably the fact that you can use different backends and these use cases are also important?