Here’s the thing. It is actually quite clear to me that the liberal interpretation of the tactic works, and isn’t a problem. I will attempt to lay it out for everyone, and then show why it isn’t broken or bad.
We all know that lightfoot halflings have a special ability that allows them to attempt to hide behind a larger creature. This is a specific vs. general rule that overrules the normal limitations on attempting to hide. Any argument about “knowing they are behind the fighter or behind that tree” is moot, as that has nothing to with the tactic.
Let’s be clear what this actually means. The lightfoot halfling is using that larger creature to become “hidden” so their intended victim can’t technically see them. Let’s say the lightfoot halfling was successful. We all know that the intended victim just *knows* the lightfoot halfling must be somewhere behind the larger creature, but what really matters is at that moment, they cannot actually see the lightfoot halfling. Once it is true that the intended victim cannot technically see the halfling, we look at the following rule: “When a creature cannot see you, you have advantage on attack rolls against it.”
Being able to duck behind the same fighter and attempt to hide again (or ducking behind a large pillar for full cover) is a legitimate tactic, not because the rogue trying to convince people that he's not right behind the fighter or pillar (they can target that space with attacks all they want)... but because he's trained to be able to take advantage of being hidden so that when he does attack from hiding, his enemies can't properly gauge how he's going to attack next. Like a previous poster said, it's like trying to hit a fastball being pitched from darkness.
Done. The only argument against this is that someone doesn’t like it.
But here is why it isn’t broken.
Getting Sneak Attack almost every round is not broken. Rogues don’t get Extra Attack like the “warrior” classes. Sneak Attack is necessary for them to be competitive, damage-wise. They actually get Sneak Attack very easily as long as their victim is also being harassed by another adjacent enemy. Becoming hidden is just another (more traditional) way to get it. It’s also harder to get because it takes an action and a skill check to attempt it.
Getting Advantage is one of the other specialty tools of a rogue. Advantage is not a bad word. Not even for lightfoot halflings who hide behind larger creatures, or for wood elves who hide when they are lightly obscured by natural phenomena. For those who are concerned about rogues getting advantage too often because they have more critical hit opportunities, look at the larger picture.
They actually have 2 paths towards getting 2 attack rolls per round to trigger critical hits. It’s a choice.
They can either use their bonus action to attack with two weapons to have 2 chances to crit, or they can use their bonus action from Cunning Action to make a Dexterity (Stealth) check to try and get advantage, which is also essentially 2 rolls to try and get a crit.
It is all built in, and balanced.
… in my opinion.
[Edit: forgot a word]