  Dark matter-baryon scaling relations in galaxies are important in order to
constrain galaxy formation models. Here, we provide a modern quantitative
assessment of those relations, by modelling the rotation curves of galaxies
from the Spitzer Photometry and Accurate Rotation Curves (SPARC) database with
the Einasto dark halo model. We focus in particular on the comparison between
the original SPARC parameters, with constant mass-to-light ratios for bulges
and disks, and the parameters for which galaxies follow the tightest radial
acceleration relation. We show that fits are improved in the second case, and
that the pure halo scaling relations also become tighter. We report that the
density at the radius where the slope is -2 is strongly anticorrelated to this
radius, and to the Einasto index. The latter is close to unity for a large
number of galaxies, indicative of large cores. In terms of dark matter-baryon
scalings, we focus on relations between the core properties and the extent of
the baryonic component, which are relevant to the cusp-core transformation
process. We report a positive correlation between the core size of halos with
small Einasto index and the stellar disk scale-length, as well as between the
averaged dark matter density within 2 kpc and the baryon-induced rotational
velocity at that radius. This finding is related to the consequence of the
radial acceleration relation on the diversity of rotation curve shapes,
quantified by the rotational velocity at 2 kpc. While a tight radial
acceleration relation slightly decreases the observed diversity compared to the
original SPARC parameters, the diversity of baryon-induced accelerations at 2
kpc is sufficient to induce a large diversity, incompatible with current
hydrodynamical simulations of galaxy formation, while maintaining a tight
radial acceleration relation.
