If Middle Earth had guns, Gandalf definitely would have carried an AK instead of a stick.
Tolkein fought in WW1, it's no wonder he romanticized a time when wars were fought with swords. His war was a meat grinder over literal inches. Just waved of bullets and bombs that killed indiscriminately.
So he built a world where combat was about skill and one highly trained and motivated person could beat 100 enemies face to face
The people in WW1 with the highest kill counts were the ones that spent 12 hours a day loading shells into artillery miles from the fighting.
If you write it down you have to pay attention to it.
Back filling as you go is easier, and the other players can hold min maxers in their place as well as a DM.
Like, I never played much but we knew a dude who would always claim undisclosed knowledge or experience relevant to whatever was happening. So eventually in-game we just started calling him a liar, and the DM went with.
For example we needed food so he suddenly was an expert in foraging, but he really wasn't so no one else ate the berries and he had severe diarrhea the next few game days.
It's self regulating, don't try stupid shit or stupid shit happens to you.