I disagree. I think the term is well used in circumstances like the 376 or 458/4 where provision of that fleet means that the trains involved require separate management for use on a common set of services, imposing additional parts and training obligations on the operator.Goldfish62 has brought up something I'm forever moaning at people about -- calling fleet microfleets when they're not.
I think "microfleet" has to be one of the most wrongly overused terms on this forum. In threads discussing future Southeastern fleets, Class 376 and 458/4 get described as microfleets often, for example, despite being 36 and 28 strong fleets! Working alongside a very large fleet (465s) does not make them a microfleet.
In these cases, it is not the absolute size of the fleet that counts, but the impact on operational management.