Gunpla kits (at least the modern ones) are designed to not need painting or glueing to complete. Building a kit according to the instructions is referred to as a "straight build" or "out-of-box" (OOB) build. Anything more than that, from painting to kitbashing, is often called a "custom build" or just a "custom".
To answer your question, there are definitely modellers who do more realistic custom builds and use military modelling techniques like weathering etc. Some builders create works that have a deliberately gritty or diesel-punk style, but as far as I know there isn't a specific term for this style or those who build in it, at least not in English.
I think in terms of a comparable aesthetic tone, the gunpla equivalent of some-one like John Blanche would be Kazuhisa Kondo
, Makoto Kobayashi
or Kow Yokoyama
(who created Maschinen Krieger
If there was enough interest in the topic it would probably warrant a thread in Painting & Modelling.