On a reaction that requires only a verbal component, you can force disadvantage onto an enemy and grant an ally advantage. This first-level spell allows you to hinder an enemy and aid an ally at the same time for a very low cost. And it isn't limited to an attack you can do this for an ability check, or a saving throw. There are a lot of people that don't understand how to play this game strategically, and I am not advocating for power gaming at the expense of roleplay. I am simply stating that some people do not understand what features are strong and what features are weak, I think you are one of those people.
I'm speaking purely as a powergamer with extensive experience playing from 1 to 20 with epic boons. This is a balance discussion, roleplaying isn't relevant.
I understand perfectly well what this spell is capable of. The problem here is that one of us has extensive knowledge of Fifth Edition and the other doesn't. I think we would both agree on that, it's just that you're wrong about which of us is ignorant. You are lacking some very basic principles of powergaming in your assumptions here.
Shield gives you plus 5 to armor class nothing more nothing less. If you are facing intelligent enemies or spell casters they can opt to make you roll a saving throw instead of attacking you or just attempt to grapple you bypassing shield. Shield is an amazing spell, don't get me wrong but it does not scale nearly as well as Silvery barbs. When you get to higher tiers of play, it's much more likely that you will be hit regardless of whether you shield or not because the attack modifiers are too high on the enemy, which is why health scales way better than armor class. You just don't know what you're talking about here. Advantage and disadvantage on any aspect of combat is so domineering, to call that niche shows a laughable misunderstanding of how bounded accuracy affects combat in 5e.
On the contrary, Shield scales extremely well. AC has accelerating returns. +5 AC for the entire round. The higher level you are, the cheaper the price gets and the better shield becomes, and the worse Silvery Barbs becomes. I know, I know, you don't "get it." I'll actually break this down for you.
At high levels if you build for AC, bounded accuracy means that you can just count entire ranges of CR out of the fight, because they can only hit you on a 20. If they do? Well, sometimes you get hit, HP is a resource. If they critically hit you and it really hurts? That's why you take lucky. If you think it's better to use Silver Barbs to "force" one miss, if you even think Silvery Barbs is even in the same category as Shield in terms of mitigating incoming damage, you just don't know what you're talking about. So let me share a very basic principle of powergaming that someone who seems to view himself as such an authority on min-maxing should know:
action economy wins fights.
You assert that at higher tiers of play attack modifiers are so high that +5 AC become effectively irrelevant. That's nonsense. So what sort of fight are you expecting, here? That's kind of important to know if you're going to discuss what's effective and what isn't. Are you assuming basic, medium-hard difficulty fights with one or two creatures that don't have legendary resistances? If you're only up against a couple creatures, you're going to smash them with or without Silvery Barbs. Or you should. In a fight that's actually dangerous, a single beefy target is going to have legendary resistance (which Silvery Barbs doesn't negate), and you're going to have a pile of mooks to handle. Alternatively, for battles that aren't boss fights, an assumption I am baking into my thinking is that you are going to be faced with large numbers of enemies. If you aren't facing off against enemies in numbers, if you really are just fighting one big thing that makes one or two big attacks, Silvery Barbs has a larger impact. That's also not a style of play that is especially challenging. Tilting a
single attack, or saving throw, or ability check is not on the same level as decreasing the number of attacks that connect from "not many" to "almost none." Shield is a much more economical spell, and will dramatically outpace Silvery Barbs in mitigating a large barrage of enemy attacks.
Silvery Barbs uses your one reaction for the round, which means you can no longer cast Shield (uh oh), and you can no longer Counterspell (BIG UH OH). That is a tremendous opportunity cost. What do you get out of it? Well, it depends. Sometimes you can save a buddy who botches an important saving throw. That's good. Sometimes you try to do that and it doesn't work out, and then you're down a reaction. Sometimes you can make an enemy fail a saving throw. But that's the thing... one enemy. One ally. One attack. Even if we operate under the faulty assumption that Silvery Barb always turns a roll the way you want it to go, instead of just tilting the dice 3-4 points in your favor on average for a
single roll, the impact is always limited. In order for it to be "broken" as people keep repeating, it would need to tilt entire fights. One key roll being reverse
can tilt a fight, but it's not something you can rely on.
Intelligent enemies? Doesn't matter how smart they are if they rely on attack rolls. Grappled or not, most creatures in the published books need to make attack rolls to deal damage, that's the win condition of most monsters. Someone competently building an AC tower can shrug off a large part of the main way things damage you. Saving throws are a thing, yes, but they are less common, and against spells what you want is probably Counterspell more than Silvery Barbs. That said, there are cases where Silvery Barbs would be handy. It isn't isn't nearly as many as you are asserting. At this point you're probably just going to keep asserting it more because people never admit when they're wrong rather than because there's any truth behind it.
One roll
can be made to miss you. One. I'll grant it's versatile, you can also allow someone to remake a save, or ability check. That's handy. That's why it's a
good spell. If it only impacted attack rolls it would be pretty weak, so it's good it can impact more than that.
You're just going full tilt Dunning Kruger Effect now. Again, I just think you don't know what you are talking about. Silvery Barbs is better than some 4th level spells, and only gets stronger the higher the party goes.
Better than 4th level spells? Come on now, even you can't believe that. If you do, you really should stop accusing others of suffering from the Dunning-Kruger effect. Quick compare and contrast time: Silvery Barbs, force a reroll using your reaction; Polymorph, your ally can go from injured to being a giant gorilla. You're going a bit agro and dipping into the hyperbole. It doesn't make you look like you know what you're talking about when you fling out insults rather than making arguments.
You're the one who doesn't have an understanding of how powergamers think. It is very rarely powergamers who knee-jerk whine about things like this.
A massive false equivalency, sleep is a great spell early on, but there is a lot of counterplay for it. The easiest one to spot is the health pool which, 5d8 ceases to be very effective when you leave the first tier of play. The second is that it does not work on creatures that are immune to charm or undead. It also does not work on elves. Sleep is a great early game spell but it tapers off a lot sooner than shield.
My point, you missed it.
The point is that if you disingenuously (or hell, even sincerely) misrepresent a spell by highlighting its best use-case rather than how it plays in practice, you can make spells that are totally balanced, like sleep, seem broken.
Another egregious false equivalency. Web allows the enemy to make a dexterity saving throw, so creatures that are proficient or have magic resistance are going to fare much better with this. Web can be removed with fire. There are also creatures who are immune to the restrained condition such as Shadows. There is meaningful counterplay to Web. Silvery Barbs doesn't even grant the target a saving throw, it just happens. The only way to thwart it is to counterspell. They are different kinds of spells but if I could only take one of them, I would go with Silvery Barbs because it is busted.
Again, my point, you missed it.
Though I actually think web is a really good spell. The point, again, is that it's easy to take the best case assumptions for a spell and conclude erroneously that the spell is therefore broken.
I don't believe you to be a bad actor, you just don't know what you're talking about. I don't hate Silvery Barbs, it is just objectively overpowered. If that doesn't bother you that's fine, your table is your table. But I would not hold it against any DM who banned it from play.
"Objectively"? No.