>The entire point of using diamonds in wedding rings is for the male to signal how committed he is to the marriage by expending a large amount of money on both the ring and the wedding itself. It then acts as a way for the wife to signal her status to other women by showing off how much her husband was willing and able to spend on the ring.

That's some nice historical background (which could be post-hoc contextualization that fits certain agenda), but traditions have this weird habit of outliving their actual purpose and still having the form without the role.

So no, you don't have to commit to traditional gender roles to have diamond rings and don't have to make them expensive as otherwise it's not doing the thing it's supposed to do. The could just not do the thing at all and you can still have them.