You have it backwards. Deflection = deviation from the normal path. Less deflection = less deviation = less "curviness" = larger circles.
These ions are initially traveling in a straight line. Due to the magnetic field, an equal force acts on each ion. The heavier ions (purple) are accelerated less due to their higher mass. Therefore, they are deflected less, and follow a trajectory with a larger radius (imagine if these trajectories formed a circle: the purple circle will be larger (larger radius r) and the green circle will be smaller (smaller radius r).
Yes, the logic for the second explanation makes sense as well.