don't know what to say to you, the notion that CSSJB = the full power of SSJB, is literally the factual reason why its so strong. There's no other explanation given to its strength. If you want to argue that SSJG - SSJB combo would just be as strong, you'd be right. But Toyo's dog shit at writing his own story.
No, it wouldn't be right. They are two completely different things. CSSJB is differentiated by sealing the aura and therefore the entire power of Blue within the body. Using Blue in bursts does not seal the aura, therefore it is not sealing away all of Blue's power. At best the burst form of SSJB is a more efficient version that takes advantage of more of its power without losing much stamina. Compare the statements:
Ch. 22, pg. 25.1-3
Context: Goku and Trunks continue to observe Vegeta fight Goku Black
Trunks: “That’s amazing…! How could he possibly…”
Goku: “
He’s storing the power of Blue until the right time and lets it explode when he needs it.”
Kaioshin: “Is that the same thing you did back when fighting Hit?”
Goku: “Yeah, but in my case, I could only go as far as making the switch once while Vegeta is able to repeat it over and over again. Furthermore, his power isn’t decreasing. That just shows how hard he’s trained.”
Ch. 24, pg. 36.1-6
Context: Goku and Zamasu appear to be fighting evenly
Trunks: “Goku… This is amazing… He’s fighting equally with Zamasu…!”
Vegeta: “Kakarrot…
He managed to seal the Blue’s overflowing power within his body.”
Trunks: “What…?”
Vegeta: “Blue’s weakness is that its full power lasts only for a short while. He faced that weakness and overcame it.”
Trunks: “So that means right now, Goku is…”
Vegeta: “Goku is continuously fighting at 100 percent. Finally, he has completed Super Saiyan Blue.”
Storing its power and sealing its power are two completely different things. How I view it is that Blue Bursts is the maximum you can get out of Blue without sealing the aura away.
Merged Zamasu isn't in anyway massively stronger than Goku Black, you can make that argument but the actual fight shows that even a tired Super Saiyan Blue with hardly any energy is capable of piercing this idiot. His epic performance was against two tired Super Saiyan Blues running out of energy, impressive.
Vegeta wasn't tired at the beginning of the fight. He was briefly knocked out of SSJG but aside from that had taken no damage. He was immediately destroyed when he used Blue. The only reason why Goku's attack pierced Zamasu is exactly as you said, because he's an idiot. He was so arrogant that he didn't even put up a defense against it. There's no reason to read further into it than that.
I think it's telling that Vegeta didn't even attempt to use SSJB in bursts against MZ. He was able to get away with using SSJG against a far stronger opponent in SSJR Black, but MZ was far too strong to make it work. If his Blue power was really on par with Zamasu there's no reason why he wouldn't give it a shot. At least he'd be able to manage something instead of getting one shotted out of Blue while fresh:
Vegeta was also willing to put aside his pride and fuse with Goku to get the upper hand on him. They could have both taken half of a senzu bean and taken him down easily if he was only Blue level, but Vegeta knew fusing was the only option worth trying.
And finally this:
Ch. 27, pg. 15.6-7
Context: Beerus observing Vegeta’s training
Beerus: “What’s up with him? He’s more into this than usual.”
Oracle Fish: “
It must be because Son Goku was stronger than him during the battle with Zamasu.”
Beerus: “Ah… It’s a stupid rivalry--not worth my time.”
Goku was stronger despite being equal?
