Prism
Explorer
Long story short, +1 studded and mage armor give the same AC. If you manage to get your hands on +3 studded leather, even better, but that's not necessary.
There's also the issue of the time: Mage Armor lasts for 8 hours, and sooner or later you will find yourself in a fight with no armor whatsoever. So it's a purple spell, with the possiblity of obsolescence and the time it lasts keeping it from being blue.
It depends on how you allocate magic items. If you simply use the item description then studded leather +1 is rare like all +1 armour. However if you also use the treasure tables as an indicator then the good magic armour like studded, half plate or plate is incredibly rare and only appears on the top tables. You have less chance of finding +1 studded than you do of finding a staff of power. A holy avenger is more common than a +2 set of studded armour. All designed to keep AC under control