Normally, 16 bit signed integers are used.
Perhaps the least significant bits are useless, but you can ignore that.
The gyro produces an integer of 16 bits, but that does not mean that all 16 bits are accurate. Perhaps only 9 to 12 bits are useful.
One device is measuring acceleration and the other measuring rotation. It's like comparing apples and cheese. Your belief that they "should have the same resolution" is misconceived.