I don't know what you mean by "the metric they like to see in terms of CTR". Maybe you are trying to say "what CTR should I be achieving" or something like that.

Let's understand something. The biggest chunk of quality is CTR which is something that is measurable. QS is not something that's picked out of thin air. In search, your CTR is compared to that of others for the same keywords and a relative number - your QS - is calculated from that.

If you create a campaign properly and separate your search campaigns from your display, you'll notice there is no QS shown, even if you use automatic placement with keywords. Why would that be? Simply because in search, Google is dealing with one site. It's the same all the time, at least, it's controllable to be the same for every advertiser at any one time.

In a content campaign, they have no control. Sites display ads in a variety of ways so you can't compare the CTR you get on one site against that of another. There's just too many variables which are themselves variable. Google still needs a measurement of quality and that is still CTR but now this is calculated on a site by site basis (and likely for text vs image ads too as well as other things) because the same ad on one site may get a vastly different CTR on another, yet still be of the same relative quality as a competitor's ad. So you still want higher CTRs in display campaigns but look at it site by site, not for the group where your ads may be displayed on many sites.