I did not comment on that at all yet, my comments where only external MD vs. all te rest of the types.
The usage of virtual MD types depend on your business requirement, not on where you load from
If for example you have MD types for Product and Customer. And you have a product group and Customer group. And if you than have an attribute which would be relevant on level product group - customer group, than it can make sense to work with virtual MD type, if you e.g. want to manually maintain it or if you have issues loading on the most detailed level of product and customer.
Yours
Irmi