On the arrows there are acid arrows and fire arrows but they make surfaces and don't just add damage like BG2. I don't actually have a problem with these items, they seem like legitimate homebrews items.
The issue is with the homebrew 'dip' rule. You drop a candle on the ground, dip your sword / arrow into it and you have a fire arrow. So something magical has become something mundane. Now, flaming arrows have been used in real medieval combat but they were just set up differently -- wrapped in cloth and the like.
Similarly with 'mundane' flaming swords. If you watch the 'making of' documentary you will find out that HBO's game of thrones went through multiple flaming swords in their filming because once you light a sword on fire with sterno or the like it ruins the sword. They eventually developed one that could remain lit for two minutes and could be reused.