Yes, most tools can currently only be applied to the entire model, and we do not have an editor-wide vertex/edge/face selection. The reason UE can do in realtime what standard DCC tools can only do offline, eg render millions of objects comprising hundreds of millions (sometimes billions!) of effective triangles in the viewport at 30-60fps, is that the objects are stored in extremely optimized/compressed forms that cannot be edited. So we have to ‘unpack’ a mesh to get access to it’s vertices/edges/triangles, and it is not plausible to do that unpacking for every mesh in the scene (in a large modern game world this could take hours and require tens-to-hundreds of GB of memory).
The result is, currently we only unpack a static mesh when you explicitly start a Tool on it, and this is why selection is only “inside” a Tool. As posted above, we are looking into ways to improve the UX here, but we do have this fundamental huge-data problem to contend with.