  Compact non-resonant systems of sub-Jovian planets are the most common
outcome of the planet formation process. Despite exhibiting broad overall
diversity, these planets also display dramatic signatures of intra-system
uniformity in their masses, radii, and orbital spacings. Although the details
of their formation and early evolution are poorly known, sub-Jovian planets are
expected to emerge from their natal nebulae as multi-resonant chains, owing to
planet-disk interactions. Within the context of this scenario, the
architectures of observed exoplanet systems can be broadly replicated if
resonances are disrupted through post-nebular dynamical instabilities. Here, we
generate an ad-hoc sample of resonant chains and use a suite of N-body
simulations to show that instabilities can not only reproduce the observed
period ratio distribution, but that the resulting collisions also modify the
mass uniformity in a way that is consistent with the data. Furthermore, we
demonstrate that primordial mass uniformity, motivated by the sample of
resonant chains coupled with dynamical sculpting, naturally generates
uniformity in orbital period spacing similar to what is observed. Finally, we
find that almost all collisions lead to perfect mergers, but some form of
post-instability damping is likely needed to fully account for the present-day
dynamically cold architectures of sub-Jovian exoplanets.
