I can't really see how a designer is going to be much help developing distributed hash tables, compilers, scalable push messaging frameworks, drivers, network analyzers, packet routing systems, load balancers, linear solvers, file systems, natural language processors, machine learning systems, and a whole host of other software that makes the world tick.
my hash table is useless if the users can't tickle the UI in such a way as to use the hash table.
That's not to say design is unimportant, just that plenty of teams are better off adding there 30th coder before their first designer. Others may be better off adding there 10th designer before there 2nd coder, but I have never heard of them.
I do not doubt that certain skills have more value than others in certain contexts but it's difficult to work on a team where the importance is emphasized.