CHEMISTRY COMMUNITY

If length and strength are inversely proportional to one another, why is it that sigma bonds are both larger and stronger than pi bonds?

Their difference in strength has to do with their overlap. Sigma bonds are characterized by end-to-end overlap while pi bonds (which occur between "leftover" p-orbitals) overlap in a side-to-side fashion.
As you can see in the image below, the head-on contact allows much more overlap and thus more strength.