I... can't agree with that. That's exactly the kind of line that you'll say after you get strong and forgot just how invaluable BP used to be.
I didn't talk about anything specific - just in general - but if we're talking about AQ4, I believe we can agree that eating two Rage Overdrives from the boss means that you'll wipe, yes? Sure, RNG might decide that one person eats all three shots, but each one might as well one-shot three people from your team. My Thunder team can these days basically eat two hits per Hime and not even die, but that's not how it used to be. Anyway, let's say that Joan will entirely negate one Rage Overdrive.
So, using Joan:
Two turns -> Overdrive turn (negated) -> one turn -> Overdrive turn (team crippled) -> one turn -> final turn (team wipes from Overdrive)
5 turns + 2 crippled turns
Using BP:
Three turns -> Overdrive turn (team crippled) -> two turns -> final turn
4 turns + 3 crippled turns
Now, when you consider the reality that:
1. Joan doesn't entirely negate the Rage Overdrive.
2. How much better BP scales with your team abilities such as damage cuts from Hime.
3. How much better off you'll be with BP if you get lucky with the boss blasts such as 3 hitting the same Hime, so your team isn't crippled yet...
It's really, really difficult for me to say that "Oh yeah, Joan is totally better." If you really need more turns, then Joan WITH BP is bloody amazing though.
So... yeah. I just don't agree with your "Joan is good enough or GTFO" -like statement. New players are going to be new, and that can't be helped. Please don't discourage them away from BP. Yes, the usefulness vastly diminishes as you get stronger, but what we can do today without BP doesn't change the way that newer players have to play. Even though they're far, far better off than I was back in the day, seeing as Grids are just a matter of bothering with Gem Quests now, it's not realistic to expect new players to have 80%+ Assault in every element.
Really though, the only way for either of us to prove our points would be to strip away an Eidolon or two, strip away weapons until you have like... 70% power? And then we're probably roughly around the entry point to AQ4 content. Then you'd just need to record a run with both Joan and a run with BP. But I, at least, am certainly not going to bother.