When I add a 775 x 775 image to a fabricjs canvas and resize it down to around 90 x 90, the image greatly loses its quality.
It should probably go for a comment, but unfortunately I am new here and I can't add comments. However, to me it looks like antialiasing issue. Canvas is just bunch of pixels - it's up to you whether you do some antialiasing or not. Browsers however do some antialiasing on picture scaling (see here Disable antialising when scaling images).
This question might be a duplicate of:
Html5 canvas drawImage: how to apply antialiasing
HTML5 Canvas and Anti-aliasing
Hope it helps.