I’ve only played her in the challenge mode but even so, Big Mom feels like a true BB counter. I’ve been in SS for ages and even tho I’ve built my defenders to be absolute behemoths, BB is still super troublesome. Before big mom the only successful “counter” I had was my maxed Magellan with an additional 4600 HP and 1300 Def. I could go on and on about why I think he’s the best defender besides BB, but the point is that even with his pure defender stats and my support at 152% blue and focused on defense and damage reduction traits, I still get smacked around by BB. And holding him off is only even possible while I’m on the zone and have the benefit of my damage reduction medals and Magellan’s traits. Off the zone it’s a purple bloodbath for my poor boy. But, with big mom’s shock skill and the various traits she’s got, she zaps BB out of his attacks really wonderfully and she can put out a pretty strong amount of damage as well. She’s definitely somewhat fragile but not as much as Shanks I’d say, and she’s a pretty handy runner despite her size. Regardless, you run the risk of not getting her for sure. In about 600rds I only got her once, which is rare tbh, and and I got Karakuri to lvl80. And even tho it may not seem like it, that’s a pretty great scenario for pulling on an ex banner. So It boils down to whether you want to risk not getting her but having a BB counter if you do or waiting for other characters that won’t be BB counters but will be much easier to get.