I'm no expert on Dungeons and Dragons, but one of the first fundamental rules I've gleaned from having played DnD games, is that, whenever you want to hurt someone, that other guy has a chance of defending himself against you. This is almost like the Golden Rule of DnD.
For example, if you slash a sword at someone to hurt him, you have to roll your attack against his AC. His AC is his defence against being cut open.
If you wish to cast a spell to hold him in place (so that your beefier buddies can pummel him later), he can make a saving throw. That saving throw is his defence against being held. And at the end of subsequent turns, he rolls his saving throw to break out of the hold. The end-of-turn roll is his defence against being held for the full duration and being pummelled helplessly.
If you wish to cast Sleep on him and his compatriots, their hitpoints are their defence against being rendered unconscious for two turns.
The game allows the attacker to make his offensive move against an opponent, and the latter has a chance to avoid it completely, or mitigate some of the damage. This is the ecosystem.
And along comes Larian's gimmicks, the invasive species.
This is taken from a fight at the goblin guard post outside the Selune temple. An all too familiar sight, I'm sure.
The fire bottle, some kind of medieval molotov cocktail, missed Lae'zel. Her AC was her defence against the impact of the thrown bottle. But she was still damaged for 2D4 from the ground effects. She didn't get any kind of defence against the latter. She was just forced to eat that 2D4 damage.
Let's compare this molotov cocktail with the Bonfire cantrip:
Spell description taken from dndbeyond.com: (emphasis mine)
You create a bonfire on ground that you can see within range. Until the spell ends, the magic bonfire fills a 5-foot cube. Any creature in the bonfire’s space when you cast the spell must succeed on a Dexterity saving throw or take 1d8 fire damage
. A creature must also make the saving throw when it moves into the bonfire’s space for the first time on a turn or ends its turn there.
The Bonfire spell creates a surface effect rather similar to the one above. And here, we see that anyone caught in the Bonfire can make a saving throw to avoid damage, which is very much unlike Larian's homebrewed molotov cocktails that force the player to eat 2D4 damage.
This is the reason why Larian's homebrewed gimmicks are an invasive species. The enemies that use these fire bombs thrive in this environment that is not built for Larianisms. The DnD ecosystem is one attack and defence. Larianisms are about attack, but not allow the other party to defend. Lae'zel was not given the chance to prevent herself from taking 2D4 damage from a missile that she dodged.
Larian needs to curb the spread of this invasive species. There's a mod on Nexus that helps with this, and I hope the modding community can do more if Larian remains obstinate on letting this invasive species run amok in this game.