Not bad.
Note d8 is average for most creatures.
Arguably, martial class training makes its trainees beefier than average, whence d10 and d12.
Meanwhile, perhaps those who immerse in magic are somewhat neglectful of their physical body.
But it all depends on class concept. For example, the Cleric maintains the average despite immersing in magic.
Also, I view the Sorcerer class as having ones own body transformed into a magical body. Thus the body itself is the source of the magic and the Sorcerer training is learning how to "pilot" this magic body. In this sense, Sorcerer is one of the few magical character concept that could have Constitution as the spellcasting ability. Depending on interpretation, the fullcaster concept could be average d8, or enhanced d10 or d12, or perhaps depleted d6.