They are not the only ones "brilliant" enough to devise such devious plans. How else do you think the sword, the longbow, the gun came into such widespread use? People saw how effective they were and decided to use one for themselves.
No, to you, apparently, the history of gunpowder was "we better NOT use gunpowder or else some omnipotent being will single us out for punishment". Your suggestion is not an honest attempt to respectfully (of the players) develop technology in your game. This isn't about the "history" of anything, this is about the DM not liking something the players are doing. Facing that, rather than passive-aggressive strategies, would be the most polite way of dealing with the problem. The "abuse" here is the DM abusing his role as game moderator in order to "teach" players that they should read his mind.
As someone said upthread, when the pcs start an arms race, they LOSE.
And so the weak appeals to versimilitude have appropriately come to an end.
All I'm saying is what's good for the goose is good for the gander.
What's good for the goose, apparently, is not playing DnD. As I said, I seriously doubt you've ever actually used this strategy as a DM. I don't know of anyone who plays DnD that would continue in this kind of game. What you're suggesting is not respectful of the players.
If a tactic is useable by pcs, it is useable by others. When the players realize that if they abuse the rules, the dm is also free to do the same, that kind of crap will not go on and the game will play as intended.
On one hand you try to justify your actions on the basis of some sort of versimilitude ("people IRL adopt successful technologies") and then nearly in the same breath you give lie to this rationalization by revealing the (rather obvious) motivation for your suggestion here - which has nothing to do with realism and everything to do with the game "playing as intended" which is really just "playing the game the way the DM wants to".
AFAICT "rules abuse" to you is just the PCs using the items in the game to solve problems. The "abuse" part, apparently, is doing it in ways that the DM didn't anticipate. If the DM thinks there's something fundementally wrong with the rule's application (one example given was that oil damage was linearly related to the quantity of oil) then the DM should change the rule instead of embarking on your TPK strategy.