  We characterize the stellar mass of J2239+0207, a z~6.25 sub-Eddington quasar
(M_1450=-24.6), using dedicated JWST/NIRCam medium-band observations of a
nearby PSF star to remove the central point source and reveal the underlying
galaxy emission. We detect the host galaxy in two bands longward of the Balmer
break, obtaining a stellar mass of ~10^10 M_sun, more than an order of
magnitude less than this quasar's existing measured [C II] dynamical mass. We
additionally calculate the mass of J2239+0207's central supermassive black hole
using JWST/NIRSpec IFU observations, and determine that the black hole is ~15
times more massive than predicted by the local M_BH-M* relation, similar to
many high-redshift quasars with dynamical masses determined via millimeter-wave
line widths. We carefully consider potential selection effects at play, and
find that even when z~6 quasars are compared to a local sample with similarly
determined dynamical masses, many of the high-redshift quasars appear to
possess overmassive black holes. We conclude z~6 quasars are likely to have a
larger spread about the M_BH-M* relation than observed in the local Universe.
