Charlaquin
Goblin Queen (She/Her/Hers)
It’s not really the length of a bow that matters but its draw weight. Sure, longer arms can increase a bow’s draw weight, but so can composition and curve. Legolas’s bow looks recurved, so it’s probably heavy for its length.Sure, "elf" and all, but the "bow in the movies" is a short bow:
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THIS is not a 5-6 foot longbow.
As for the novels, I could not tell you, it has been a long time since I read the novels and in those he could easily be represented as using a longbow.
Regardless, a STR 13 requirement for longbow (heavy weapons in general) makes perfect sense. Anyone who uses such weapons regularly will be "stronger" than your average STR 10 humanoid.
But, yeah, point is, if you want to use a bow effectively against armored targets, you need one built for a very heavy draw, and therefore need to be very strong to use it. Unfortunately, strength is far more nuanced than D&D accommodates for. The muscles one needs to build to shoot a heavy bow are quite different than the muscles one needs to build to fight with a longsword. Amusingly, I think the important muscles for fencing would be better represented by Dex than Strength, and vice-versa with the important muscles for archery.