> the Hubble telescope is practically obsolete (and indeed obsolete, since it will be de-orbited soon).

This isn't quite accurate. Hubble has ultraviolet capabilities that are impossible to achieve from the ground (due to the atmospheric absorption). JWST won't replace this functionality. Also, while AO can achieve similar or better angular resolution, it can be difficult to characterize the point spread function (PSF) of the AO system. By contrast the PSF of HST is incredibly stable. Knowing the PSF and having it be stable is key for some types of science.