As a static mesh sorry to say that is how scaling works on the local level. As you mentioned the more direct root as far as a static object goes a blend shape is more reliable and less messy as to the need to maintain the proper volume as in X always = 1 meter. The reason this works is blendshapes scales based on relative scaling, is in volume changes based on worldspace in relationship to other objects around it, where local scaling changes the scale of the object based on it’s own relative size in world space.
The only problem is in general most objects are reference by their local transform and if you change the relative scale of the object via vertex manipulation the world space will still read the object scale as when it was first imported based on it’s local scale.
This effect may or may not be an issue but could be a problem with rendering engines that makes use of real world models, like lighting cloth simulation and physics, as most models are based on the local scale of the object and do not take the relative scale into account. Something to keep an eye open for.
If a vote I say go with the blendshape approach as it just works with out having to get fancy.