I'm sorry, but if you are an archer, hide behind a barrel... you can't pop out form the barrel and shoot an opponent *who knows you're behind the barrel!!!* and expect it to work. That's too much cheese. Now if you hide in the bushes, spend a round repositioning, then fire from a completely different spot - a spot the enemy is NOT expecting you to be - then yeah, that does work.
This debate goes round and round and round, doesn't it?
One question is whether "knowing you're behind the barrel" negates the mechanical advantage of coming out of stealth. I suspect if you went invisible and then popped out of invisibility you'd be ok with it, but really what's the difference? That in once case the enemy knows where the arrow is coming from and in the other he doesn't?
Ok, what if you're standing on a 3' diameter pillar, surrounded by lava, and you go invisible. Should you get Advantage if you shoot from Stealth? I mean, the enemy KNOWS YOU'RE ON THE PILLAR, right?
Let's look at Blindsense vs. Blindsight: with Blindsense you know where your enemies are, but you still attack them from Disadvantage because you can't actually see them. Well, this seems like it's the inverse case: the enemy knows you're behind the barrel, but can't actually see you. You wait until he blinks (or, more reasonably, glances away to deflect an incoming blow) and then you pop out and ZAP!!!!
Why does it work? Well, why should ranged attacks coming out of stealth during combat *ever* get Advantage? I'm not sure I have a good answer to that, but they do, and given that they do I'm not sure I think this case is any less probable.
Another way of looking at it is that if the presence of bushes, as you describe, or perhaps more barrels, or really just any way for the rogue to change location once stealthed, if any of those things suddenly make it ok, then we've taken a nice, generic rule that works well in theater of the mind and all of the sudden introduced messy tactical complications. "Ok, how far away is the other barrel? What's the maximum distance for me to be able to get the mechanical benefit? Well how about the chest, then, can I use that? What do you mean too small?" Etc.
Honestly I don't want to have to worry about those things, and doing so really isn't in the spirit of 5e. It's really much, much simpler to simply rule "If you have full cover you can Hide, and if you are Hidden you can roll Stealth when you come out of Hiding, and if you succeed you can then attack with Advantage."
Now, I still think this is cheesy, especially if you do it over and over again every fight. It just feels like abuse of mechanics. But whether or not it's "realistic" (in the sense that anything in D&D is realistic) I think depends on whether you distinguish between
knowing where somebody is and
actually seeing them, and if that distinction impacts the stealth rules. (I think it does.)