Well; a trash mob is basically just a badly designed combat encounter. Even a game with a good combat system can have trash mobs if the encounter design is shit.
That's why reducing it to such a simple meme label as "trash mob" is so worthless. When talking about whether the combat in an RPG is good or not you have to talk about:
- Itemization
- Exploration
- Area design
- Encounter design
- How the game manages player psychology (Attrition, resource management, etc)
- Power curve / progression curve
Imagine you're in a dungeon trying to return to town and you have half of your party dead, and your surviving characters are all Poisoned so that every time they take a step on a new Tile they receive damage, and to boot you're all out of magic spells and all out of healing potions; and just when you're about to reach the safety of the town hub you get an encounter that includes enemies that can steal turns or can ambush you, and you're deathly afraid of losing this party because you
just finished raiding a dungeon floor that you had never braved before and you got some great weapons/items that you do NOT want to lose...
Perhaps in another moment when you're at full power those same enemies are an encounter you would've considered "trash", but now because of the current player psychology that I described they are of PARAMOUNT importance to your party. The subject of whether an encounter is "trash" or not is a deeply nuanced one, my friend, and that is what I wish the anti-combat people would understand.
You simply cannot reduce combat mechanics down to something binary like "trash/not trash".