  An extensive catalog of spatially-resolved galaxy rotation curves and
multi-band optical light profiles for 1752 observed spiral galaxies is
assembled to explore the drivers of diversity in galaxy structural parameters,
rotation curve shapes, and stellar mass profiles. Similar data were extracted
from the NIHAO galaxy simulations to identify any differences between
observations and simulations. Several parameters, including the inner slope "S"
of a rotation curve (RC), were tested for diversity. Two distinct populations
are found in observed and simulated galaxies; (i) blue, low mass spirals with
stellar mass M* < 10^9.3 Msol and roughly constant "S", and (ii) redder, more
massive and more diverse spirals with rapidly increasing "S". In all cases, the
value of "S" seems equally contributed by the baryonic and non-baryonic (dark)
matter. Diversity is shown to increase mildly with mass. Numerical simulations
reproduce well most baryon-dominated galaxy parameter distributions, such as
the inner stellar mass profile slope and baryonic scaling relations, but they
struggle to match the full diversity of observed galaxy rotation curves
(through "S") and most dark-matter-dominated parameters. To reproduce
observations, the error broadening of the simulation's intrinsic spread of RC
metrics would have to be tripled. The differences in various projections of
observed and simulated scaling relations may reflect limitations of current
sub-grid physics models to fully capture the complex nature of galaxies. For
instance, AGNs are shown to have a significant effect on the shapes of
simulated RCs. The inclusion of AGN feedback brings simulated and observed
inner RC shapes into closer agreement.
