Your feedback is gold! The zooming feature was in my head at one point, I have to check my list if I noted it already, just to make sure it doesn't get lost.
In which browser you are playing? Chrome might be your best choice performance-wise. On my MS Surface I can see my browsers fighting with all the transitions. Is this also so moment (when Cards "spawn", zoom and resort) where it gets hairy on your machine? Tbh, I think packing it won't change performance so much in my case - game code is all based on the native browser tech stack, so running it in a browser is already the best option you have. But maybe I can offer a version where I leave out all the CPU-intensive transitions - so cards would "just" appear without flying around. It takes away some of the information (where does the Card come from) but would lower the performance impact significantly.
Thank you for your expressing all your impressions and ideas - it's all highly welcome!