James Gasik
We don't talk about Pun-Pun
AC pretty much caps out at 20 for monsters, right? My highest level character was an archer with a +1 bow, 20 dex, and fighting style for something like +12 to hit and on-demand advantage for at least one shot a turn, and that's without factoring in if I got a buff or Bardic inspiration or something. Fought an adult blue in Storm King's Thunder with an AC of 19 and the Cleric, who couldn't get close enough to do much else, just threw up Bless to help with the party accuracy and saves, and with +1d4 to hit from a lousy first level spell, I didn't miss once (+19 with advantage, +14.5 for my second attack). So I don't really see accuracy as a problem.Except that a Flame Tongue doing +2d6 fire damage trades off accuracy, as it is not a +3 weapon with +3 to attack and +3 damage. Versus lower AC opponents, yes the Flame Tongue is very good. Versus higher AC opponents, or those with Fire Resistance which is not uncommon, the benefit is not so good.
Maybe if you have to put up with disadvantage, but most things have pretty reasonable AC's and advantage is pretty easy to get in the game. YMMV, of course, but being able to hit things has rarely been a problem that I've seen in 5e.
Now, if, in your games, you strive to keep numbers sane and you don't let people have belts of strength and +3 weapons and your players stick to fairly normal characters, that's fine, but I'm pretty used to my players rarely missing as it is, so I really don't see how a little more accuracy for a melee warrior would be an issue.