Maxperson
Morkus from Orkus
It's not a good point. Max is conflating thinking and knowing and thereby having the DM claim dominion over what a character thinks and by extension what the character attempts to do, both of which are the player's role. Intelligence checks are for resolving tasks to recall and deduce (when those tasks have an uncertain outcome and a meaningful consequence for failure), but the DM can't call for any ability check unless the players have described what they want to do e.g. "I try to recall the weaknesses of trolls based on my life growing up near the Trollhaunt" or "I try to deduce if trolls are vulnerable to fire based on available clues."
It's not conflation. Your argument is semantics. When you always "think" the correct answer, you are effectively having your PC know what those things are and trying to justify it by calling it "thinking" instead of "knowing." The only way around that sort of behavior is for the DM to enter an arms race with the players and just change up everything or at least a large portion of things.
"I try to hit the troll with a lit torch" does not require an Intelligence check before the action declaration can be deemed valid. That's a pure authoritarian power grab by the DM.
The power grab is by the player who up until that moment, used his much more powerful sword that is still at his side. There's no good reason that absent the attempt below to give the PC knowledge that fire is more effective, the PC would use the torch as his go to weapon against the troll.
However, a player so inclined could - before attempting to hit a troll with a torch - try to recall lore about the weaknesses of trolls, possibly make an ability check at the DM's behest to resolve the task, fail, then decide to attack with an arrow instead.
If the DM isn't being adversarial and entered into an arms race against the players, there is no appreciable risk here.Or the player can choose to have the character attack with the torch anyway, taking a risk that this is a good tactic against this troll right here and not a bad one because the DM changed the stat block.