We have both, and I'm really glad we do. A good QA team tests more than just "funtionality" and "usability" -- they test the product in its entirety, and notice

We have both, and I'm really glad we do. A good QA team tests more than just "funtionality" and "usability" -- they test the product in its entirety, and notice all sorts of things that non-QA people would miss. Our QA people also often poke the database and look at REST request/responses too. I think going without this kind of full spectrum testing is just shooting yourself in the foot. You can totally do continuous delivery but still use a QA team.