I think what that person is saying is that in your example the left part would probably be more durable because it is flexible and that the part on the right is less durable but more rigid, basically saying your result is expected and makes sense if you are wanting durability over rigidity.

I think that the part that is unclear is that OP is using durability, rigidity, and strength as they are defined by material science not in common English and they way they differ in definition makes that comment make sense. I’m not a material scientist though so I could be wrong.

I hope that is correct and makes sense hah!