The mere fact that OP is still wasting time debating the merits of investing in engineering over design is a dead giveaway that he has not a clue. The debate has been dead for quite some time now.

Let me clarify this for those not in the know:

Unless you're in the business of selling design services, under no circumstances should you ever hire a full-time staff designer, never mind considering them for an equity-sharing position at the outset of your enterprise.

If one doesn't know what should and shouldn't be hired for in the early stage startup, one shouldn't be wasting their time pontificating about it. OP is a moron.