Inertia is important relative to a gust of wind. It's not about momentum, it's about the wind's ability to move the rider...
Yes. I was using steady 'wind' (even though I quoted poorly).
Anything that creates a force imbalance (a gust of wind, for example) will affect the lighter rider more. But note that the converse is also true: when the wind lets up, it's easier for the lighter rider to speed back up.