In which view are you observing the Camect feed? The resolution in the multi-camera view is limited. To view at higher resolution, you need to click on the "pop-out" icon at the top right corner, and you might need to go through two steps of this to get full resolution rather than just "higher resolution". On a nest camera I think it will be just one step though.
What's being recorded should be exactly what you get if you view the nest camera using their web interface, since Camect works by recording the web feed. When there's no motion, the Camect video is at a reduced frame rate, but during periods of motion it's exactly what comes from the camera and should look the same.
If the full resolution view still looks less detailed than what you get from the web, try exporting a clip and see how that looks when played with a video player. Checking that will eliminate many different factors that come into play when viewing live, and should confirm that what's being recorded matches what's coming from Nest.
What you get when you view via the UI depends on the network between Camect and what you're viewing on, the ability of the receiving device to play the video data, and how busy Camect is doing other things when you're viewing. However these factors affect frame rate more than they do resolution -- so if you're bumping into limits most likely you see jerky motion rather than reduced resolution.
One other thing to check when viewing live is to see whether or not there's a little "cloud" icon at the top left of the camera overlay. If there is, then something about your network is preventing webRTC from working, and encrypted data has to be relayed via a proxy because a direct connection could not be established. That will also reduce the quality of the video you get.