How do you want to fix that? This is an ingrained part of the entire system in BG3 which depends more on environmental effects and barrels than actual D&D combat.
Part of me alsmost doesn't want to fix it, it's funny and resourceful, at least in this one example. But no seriously, killing a dragon this way feels totally a cheese move. How to fix it? Well for one you could make the Dragon at this juncture woundable but unkillable, triggering the Gith to flee or the conversation to go differently. I am not saying that is the best way to do it, structurally I think there are more fundamental fixes to be made, but in this one example it would be "a fix".[/quote]
The dragon is just a more extreme example, but the problem is the system itself which depends more on environmental effects than actual D&D combat. You might fix it for the dragon, but then players will just do this cheese to something else. The problems are the barrels, the falling objects, the puddles, etc.
