Shoes are designed to follow the natural, at rest shape of your foot.

If you relax and place your foot on the floor touching at the heel and ball, your toes are likely not touching. So, the arc of cycling shoes reflects that.

Otherwise the same goes for cycling shoe as any other shoes, comfort trumps all other factors. It's especially important with cycling shoes because there's little to no foot movement, so if there's any pinch or pressure point, you don't have movement to maintain circulation or relieve the pressure, and you'll suffer pain, numbness, cramps or some of all three.