As others have said, flame arrows are not particularly useful against individual opponents, they're used for setting objects on fire. On the other hand I made a flametongue bow that adds 1d6 fire damage to any arrow it shoots because I'm not overly concerned about real world logic.
If you don't want a magic bow the real issue is to me that we already have alchemist fire that sells for 50 GP per flask. I could see adding alchemist fire arrows but considering how much more useful they'd be I'd also make them more expensive. So 75 GP, add 1d4 fire and dex save or start burning (continue taking 1d4 damage until you take an action to put it out)?
It's something I notice any time I play an archer and run into creatures that are resistant to piercing damage or who have vulnerabilities/special effects with fire. Getting access to
firebolt is super easy, but if you don't want to fumble around with oil or alchemist's fire (which are improvised weapons in 5e, making them even less viable), you have no solution outside of magic. And it's almost always been like this (save for 3e, which had fairly robust alchemical items). I asked my DM about fire arrows, and even offered him that YouTube short to explain what I was talking about, and he might let us make a few during downtime, but the idea that something like this isn't standard equipment strikes me as insane.
There are creatures that ignore arrows. There are creatures you want to use fire against. But apparently there's no market for adventuring gear to help solve these issues. I thought we were past the "niche protection" era, lol.
As for how effective a fire arrow like the one in the video would be, I honestly would be happy with 1 frigging fire damage lol. It would be nice to ignite the target for some ongoing damage, but for some reason, ongoing damage is actually somewhat rare in 5e (as opposed to 4e and Pathfinder 1e, where it was all over the place), being relegated to a few monster abilities and a couple of acid spells (despite the fact that
fireball, for example, even talks about igniting things).