Just wanted to comment to the "weakness" of BM.
Well first thing we know is that Bruleé herself said that Apoo, Kidd, Capone and Urouge all already infiltrated/attacked WCI, still all of them were defeated, with ONLY Urouge being significant enough to be able to defeat 1 commander (http://mangaseeonlin...837-page-8.html)! This essentially actually underlines Bruleé's statement, that the invaders were "swiftly escorted" , as like in saying easily beaten, which in turn means, that the current worst generation is not actually able to back up their fame (http://mangaseeonlin...837-page-9.html), of course the fact of the matter remains, that we dont know, when the others attacked BMs territory, but since Urouge is still wounded, at least he could have fought BM just recently.
As such, while i still think it a bit strange, i can understand why BM "just" send Bruleé to defeat half the SHs (realising this might not do it, send Cracker as back up). The fact that BM send Cracker right away actually screams that she deems the SHs to be a bigger threat then the ones of the worst gen who previously entered! And before u say, wait u r so wrong all of the worst gen fought like hell, here is a manga page that says otherwise (and remember Bruleé already stated "swiftly escorted): http://mangaseeonlin...837-page-9.html notice: "semblance of a fight" that essentially specifically states, that all the former rookies were "fodder" compared to BMs forces, while not even being backed up by a commander and consequently it is not that far fetched when u believe 1 of ur commanders to be able to defeat (remember ONLY half the crew there http://mangaseeonlin...35-page-14.html) the SHs, since 1 commander ordinarily sufficed.
Moreover the fact that the SHs were missing for 2 years (and noone suspects Mihawk to have trained Zoro, or weatheria to teach Nami and so on) makes it difficult to judge for others, as to where the SHs stand. The fact that DD was beaten also, while being an indicator, has to be taken with a grain of salt as well, since not only did the entire country back up the SHs but also the shicki Law, furthermore there was the marine admiral around! Therefore BM might have falsely estimated the defeat of DD, not only to be the consequence of the powerlvl of the SHs but also the added shicki on the top as well as a possible interference of an admrial, making her misjudge the SHs lvl. And imo referring to the presentation in the news and the video transmission, well the admiral apologizes for whats happened to the country, being there having witnessed it all, staying in the center of destruction, ..... hmh ...... what might that mean --> perhaps he has had his hands in the downfall of DD.
Ergo BM comparing the SHs power to the ones of the SHs generation, leads to BMs misunderstanding of the superiority the SHs have over the rest of the worst gen. Therefore she made the mistake of, while having known that Cracker did not call in and say hello, not acting directly, but since the enraged army was capable of defeating Luffy and Nami anyway (which according to her knowledge meant that 4 out of 6 SHs were already done in, since Bruleé already told her she got them, so why in hell worry about the others, when even the bounty posters, tell u whom to beware of, with all the higher bounty people being in custody/dead/under watch/captured (Brook, Pedro, Sanji, Luffy) (although bounty might be misleading, in many cases it has its reference to power, or better say at least gives u a good hint)).
Of course many things in BMs crew go wrong, like having the children want to fight/kill each other or making them compare to each other, yet still as of now that all was enough to beat anyone who dared challenge her, consequently why bother? Sure as hell the fear the children have of BM also hinders her info garthering (like whom is to say that Bruleé and diesel will tell her about the poneglyph copy, also there is jinbei and luffy/nami escape being hidden from her) but perhaps she wants it to be that way, because of situations of the past, where is became clear that if she acts differently it is even worse? Perhaps she just is a believer of the way: competition is good for business?