A prerequisite was that Venus lost its solid and liquid water. As the temperature rose water couldn't precipitate, leaving it all exposed in the upper atmosphere. Oxygen and hydrogen would photo-dissociate and the lower mass hydrogen would get kicked out into space at a higher rate.
I don't think you need solar wind-magnitude energies for Venus to have lost it's hydrogen, it just sped up the process. Venus is pretty big, but it's also really hot. Venus' gravity to temperature ratio permit significant amounts of free hydrogen to be lost thermally without any solar wind sweeping it away. I think it's possible that Venus lost most of its hydrogen to thermal escape, particularly hydrodynamic escape, though today it's no longer the predominate mechanism for what little hydrogen remains.
The Wikipedia article (https://en.wikipedia.org/wiki/Hydrodynamic_escape) on hydrodynamic escape talks about escaping heavy molecules as if that's the principle function of the mechanism. But in much of the scientific literature on early Venus, hydrodynamic escape seems to refer primarily to the escape of free hydrogen.[1] I'm not a scientist so I don't know what to make of that, but in any event thermal mechanisms (i.e. Jeans and hydrodynamic) can absolutely cause gaseous particles to reach escape velocity.
[1] Photodissociation splits H2O, hydrogen is kicked out into space via thermal mechanisms, and much of the remaining oxygen, too heavy to escape at a significant rate under the local parameters, is sequestered by the molten core, volcanism, and surface weathering. At least, that's how I understand the literature as a layman. The modern debates and research seem to be centered around the particularities, especially the early geology, such as how long core material was exposed.
https://www.nasa.gov/press-release/nasa-mission-reveals-spee...