I think DAC has to win out on price not because of the price of the fiber patch but those optical modules can cost some money.

I'm getting a really bad taste in my mouth for 10GBASE-T RJ45 SFP+ modules mostly due to the god awful heat they pump out (which scales linearly with power draw): So when we are forced to use them (for example to connect to a far end that only accepts 10GBASE-T) we often cannot use any SFP cage directly adjacent.

I had the Twisted Pair/DAC/Fiber discussion with one of my an engineer that we peer with recently and they made the pitch for Fiber that "being able to see the light levels takes a lot of the guesswork out of their troubleshooting". So I do have to admit that that is one utility lost when choosing a DAC over Fiber even in a rack, but my counter is that DAC has fewer moving parts and thus a lower surface area for failure in the first place.

We have had some gear refuse to work with some DACs (just as some gear refuses to work with some SFP+ modules of various stripes) but aside from that I have yet to see a DAC that starts working stop working, while I get that with fiber runs (though usually the longer ones running outdoors) quite frequently.