JACK THE FLOORING & SISTER
If the flooring itself is noticeably sloped, such that large gaps have opened between flooring and baseboard, rectify the situation by jacking up the flooring, not the joist, until fasteners are exposed. Cut the nails or screws with a metal cutting blade. Attach a new, straight joist to the original (called sistering) and through-bolt the assembly. The sistered lumber does not have to extend into the pocket or be the same width as the original joist. Then simply re-nail the flooring to straightened, sistered joists.