Former Snap employee here (albeit 3 years ago). They care a lot about their camera, particularly speed. They do, in fact, use the "proper" camera APIs on the devices where it's fast enough, and they'll hide the latency by using a screenshot first and then subbing in the higher quality image later. But at the time this was only done for whitelisted devices that could do this operation fast enough. A lot of devices have very slow cameras.

You might disagree with how they weigh speed vs quality, but I assure you they take it very seriously.