is that their weak spot or do they simple wear on the endges, which rips them apart at higher rpm's?

Weakest part is the middle...its thin, and then the edges are next.

what would happen if you give them a ductape treatment from the inside?

Tried that then they seem to rip at the rim where they are glued. The glue will hold but the tire rips apart at the rim...hehe.

sounds like the quality of the compound isn't able to keep up..

Its just molded to thin. Needs to be much thicker.