Oh, there's also a bunch of additional places where it maybe makes sense to use PhutilClassMapQuery instead of PhutilSymbolLoader just because of the cacheing... what do you thnk?

For example, in ArcanistConfigurationDrivenLintEngine we do this:

$linters = id(new PhutilSymbolLoader())
  ->setAncestorClass('ArcanistLinter')
  ->loadObjects();

I think it's probably good to use it everywhere -- the caching probably isn't too important, but I think it's more consistent and makes intent more clear.