That presumes such a PC will always use barbs. If you make the decision to use it before the die is cast this is true, if not, then it is not.
Yes, that is what I presumed.
I included the cost of that decision as well.
This is far, far weaker and far less likely than stopping a critical hit IMO.
Clearly it is less likely than stopping a critical hit. But a critical hit happens 1 attack in 20; if you save Barbs just for that, you are going to sit around not using it most of the time.
A critical hit nullification is a 95% hit rate case; you lower the chance of the critical hit happening to near zero, and it has only a 5% chance of being wasted. The model describes it.
On the other hand, if your goal is to defeat a foe before it kills you, burning resources faster is a great boon, even if the results are less guaranteed. So I looked at its impact on going after legendary resists. And it is pretty decent at it.
Except LR is measured in integers and 1.67X1/3 is still less than 1.
I used the word average. An average of an integer value can be fractional, and its fractional value has meaning.
I could go further and calculate the variance and standard deviation of the number of LR this technique strips off, but would that actually help you? I'm serious, would it?
The point is that you can use this to strip legendary resists faster, using fewer actions, and using fewer high level slots. And once those LR are stripped, you can use it to land spells faster, using fewer high level slots and fewer actions.
Or if it was "needed" now you can't cast absorb elements when the legendary monster breathes on you or shield (or barbs) when he bites you and you die from it.
Why yes, it is using resources for offence instead of defence.
Landing one save-or-suck wins the fight. Going from a 3 round fight to a 5 round fight is going to hurt a lot. The best defence is quite often the best offence.
You are burning your reaction and likely doing it to no effect.
You burn your reaction every turn and a slot every turn, and the odds that this has no effect over the fight is low.
Quite likely, you end up with an extra LR or more stripped from the foe. Which means you win the fight, instead of not.
You are literally turning a 1st level spell and a reaction into a repeat of any arbitrary save they passed. If you can trigger
any save that they would spend a LR on, this lets you apply it faster. It is extremely good.
If there is a weak save you or an ally of yours can target with low level spells, you can strip LR very fast and cheaply.
If the weak save requires a higher level spell, you can still do it faster and cheaper than repeating the high level spell.
If the weakest save you can target is strong, it can
still brings stripping LR back into play instead of being pointless, because you can double the speed.
Using it to nullify critical hits is a fun trick, but it is a game changer against Legendary Resists.