1/2" shank are not more durable, they are more rigid. They chatter less and leave a nicer cut.

Durability with a hand held router is almost impossible to achieve. To keep the bits cool, the feed rates need to be MUCH higher than most humans can achieve. Feed rates that high require more power than is available. As a result, most all bits die of overheating. We feed them too slowly with too fine a cut and there is no chip mass to carry away the heat.

Learning how to control depth of cut and feed rate is much more important than buying ultimate high quality.