> Conferences are more important to a scientific career than an OA paper
Depends on you field of research, maybe? Paper publications make or break early biomedical research careers.
Further, the grants that these funds are paid out of often have travel funds built-in, so conferences are still available.
>Paper publications make or break early biomedical research careers.
Yes, but that has nothing to do with the OA-status of those publications - if it's a high-impact journal, then it makes the career, if it's not, then not.
Conferences are more important to a scientific career than an OA paper. The people who hire you will in all likelihood have access to your paper even if it's behind a paywall.