Big Mom does not aesthetically suit the panel. It's an awkward situation for BM to be in there since all of those pirates are dead, except Shanks who is Luffy's idol. BM was right beside Kaidou already.
All of this, but I think the bolded is the most important. She's not "cool". lol
But also, we keep seeing indicators that she's a big sister figure to Kaido. Someone that invested in his growth and took care of him. At least to the extent that a relationship like that can occur between savate pirates and adding in the usual external anime machoness that contradicts the soft fuzzy feelings the characters actually feel on the inside but are too proud/embarrased to display. She did give him his fruit, after all.
I'm not getting the vibe that Kaido had as much of a personal connection to Rocks or WB. He probably feels more affection and gratitude towards BM in particular than just respect or a competitive attitude. It's a unique relationship among the set.
Also, BM's strength is probably interchangeable with Kaido at best. The people Kaido imagined is probably the top 5 he encountered that he strikingly perceives to be greater than him. With Oden, it's probably that he thought Oden surpassed him before his death, not that Oden is necessarily stronger than Kaido right now. But he puts weight on the fact that Oden did surpass him and that his potential was probably higher.