Uh, you must not being using them correctly. The strength of an axle is determine by its outer-diameter; rigidity is to the 4th-power of outside-diameter. The hole in the QR axle causes no loss in strength or rigidity. Just bend a QR skewer by hand to see how much strength the inner core adds to the overall strength.

In the 10-years I worked in a shop, I've easily replaced 20x more solid rear-axles than QR ones. Simply because most QR axles are chromoly which is a material with 2-3x the strength of the lower-quality material used in most solid-axles. Very, very few solid-axle hubs come with chromoly axles, and you typically have to pay extra and ask for them specifically.