"And if you, and then your weight, is connected to the bike through a point that sits below this point, you must push through some leverage to tip the bike." No. The "tipping point" is the ground. Even if the BB is below the axles, there is no "leverage" to push through. It's just lower, and this has less distance to move laterally for a given lean angle. A higher BB moves further laterally for a given lean angle, which could be good or bad depending on corners (bermed, flat, off-camber).