This may be true for some, but this is also the kind of attitude that lost D&D the lead in the rpg business. Making weird arbitrary metagame designations about what a monster is "for" does not make my job any easier, it adds in unnecessary complexity and confusion and takes away from my flexibility as a storyteller. Having to strip out all that stuff to build monsters for my purposes makes my job much, much harder.
Monsters should be designed organically. Their abilities should make sense for how they function in a living breathing world, and their conception on paper should reflect a description of what they are in that world, biologically, psychologically, etc. Metagame considerations like how they will perform in combat with a "standard" group of PCs are secondary considerations at best.
The notion that "solos", "minions", and this monster role concept is somehow pro-DM or makes DMs have to do less work is insidious, divisive, most importantly inaccurate, and needs to die. Like the OP said: