I think the problem with the idea of the aberrations' monstrous forms being a punishment is that the idea is assigning morality to Magic, an eldritch, unfathomably vast mentality that could be singular, plural, neither, or all of the above simultaneously. From what we know, Magic has a flair for the dramatic, a desire to be special( or at least to not be mainstream), and allows access to power regardless of the morality of the person seeking that power. When Magic grants power to an individual, that power is inline with the person's personality, deep desires, or bloodline affinity (Assuming Magic doesn't get confused, like in Elliot's case), though not necessarily the aspects that the person wants Magic to draw from, like when Nanase kept getting sneaking spells when she was afraid of getting outed as a lesbian. Also, in Squirrel prophet, when Magic acted to give the good guys a hint to prevent a system change, it decided to do so in an admittedly half-hearted manner, intentionally giving our heroes poor odds of success.
To me, it seems the Magic doesn't care if the heroes succeed or not, just that the events are dramatic and interesting (kinda like Pandora, but broader and with a better appreciation of natural pacing). That said, the monstrous forms of aberrations/vampires could be a consequence of that. Not as a punishment, but as a reflection of the magic users and a tool to ratchet up the drama. The monsters being monstrous makes for more interesting and dramatic events. We also have official confirmation that some aberrations only have monsterous forms when using their powers, which would allow for a degree of tension building when the action is slower and sneakier.