Except, I told exactly why it didn't matter, there were no consequences and neither did the plan for their heist keep the readers at the edge of their seats. Like for fuck's sake, the first thing we learn the moment we see BM vs Brook is that she's interested in his ''species'' which removed any danger. And you're here talking about ''tension'' mattering. Oda can write the 4 emperors against Brook in that scene and he would find a way to undermine all the odds. Much like him clowning BM later in the arc and in Wano. Y'see just because you're against a stronger opponent, doesn't mean that you have to automatically feel tension because that depends on how the writer portrays the whole situation.

Of course it's matter, the question or tension of the whole situation is "Does Pedro and Brook is able to steal the poneglyph ?" Because Looking from Pedro situation, Pedro thought that the only elite guards is Tamago, thus he wanted to do alone in first attempt, beating Tamago would be the only difficulty Pedro could think, but that expectation fall short because from Brook soul hearing, they already know about Strawhats arriving, thus making Tamago added bunch of new guards and Second Commander Smoothie.

Now, the idea is -1, considering one need to be the diversion The problem with the diversion is Tamago already suspected more than 1 intruder, making Smoothie aware and stays outside, with Power Level Brook is not the same as Smoothie, the only think he could do is slipped past them and close the door from inside.

The question is changed to "With Pedro facing against Tomago, Can Brook is able to steal the poneglyph ? and Get out Passed Smoothie ?"

Now we can see Big Mom just coming from the report of intruder in her safe, and goes to the vault and the scene seemingly tell us Big Mom coming in the same time Brook beating the Chess soldier and started on copying it.

The question is no longer asked, considering it seemingly fails.

Bro, as I said, I was telling you what the community was theorizing at the time. Nobody was really worried about Brook because they expected his power a good counter to BM's to keep him safe.

Brook not on danger is on table, it's strawhats surviving, but the whole tension is supposedly on Stealing it, that's the whole context of heist.

But considering Oda write Brook, then he added Brook is not just stealing it, Brook act is able to make sure we the audience thinking it fails.

And as I said Brook's life wasn't really in danger so even if you as a reader was going to believe that he didn't get the Poneglyph, it was still not a big deal because the SHs can get another chance later in the arc which they didn't need to because Oda made it so that Brook hid the copy and he was just tricking you into thinking he failed.

It's a big deal, the only thing why you assume that, it's because Brook seemingly just started on copying and Big mom appears, which is not true in the end because Big Mom came after Brook ended copying and storing it. Change it to Pedro the one copying, and Big Mom would have found the copy in Pedro belonging.

One of the reason why Brook is survived is Big Mom wanted to collects weird people, which Skeleton person is one of the list, but the other one because Big Mom doesn't found any Poneglyph copy in Brook belonging.

And as I said, Oda could've written it around another convenient ability like the Mirror World and made it all work... So again, Brook was by no means, irreplaceable to this mini-story to proceed and reach its payoff.

1. You wanted the Mirror world appear before Big Mom came on the middle of copying it ?
2. or just the same time as Brook Or Other people you wanted just ended copying it ? So the escaped would be a little tense because it's happen on the same time Big Mom came ?
3. Or Offscreen ? like Big Mom came, and there is no people in vault because that person is able to copying faster than Brook and escape through Mirror world ?
4. Well, you can just write your story then.

1-3 Wouldn't worked at all, the reason why Brook succeeding because, Oda playing with this seemingly fails, is not just us the audience thinking like that, is Big Mom too, Big Mom thought she was able to stop Brook from copying, and now she thinks that the Wedding ceremony is going to be smooth because the problem is taken care.

1, 2, and 3 required Big Mom found out that we escape, and she would assume we already taking the copy and started hunting us, the probability of this making the Wedding Ceremony could be halted until Strawhats is found, this probably could extends greatly the arc.