Her betrayal doesn’t have to be the direct reason for his fall. She might attack his crew, or even take his poneglyphs after Luffy beats him. I think the Rox flashback will set it up even more IMO
it still would be dumb
this alliance either help Kaido and make him a more dangerous threat, or it's just dumb plot shield for SHs
the reason for the alliance existing should not be about helping SHs
I actually think Rocks past will establish the opposite , remember she was the reason he's as strong as he's today, so why their past would establish betrayal?
I actually have a crazy theory about Kaido and BM being allied for years and have been deceiving everybody into thinking they're enemies