Could you share more about how you are loading these images? I am curious if you tried loading these asynchronously by triggering the storage query for all images from a js query, and then performing a Promise.all (like this post). Curious how the timeline view in debugging looks for you i.e. are the image fetches performed concurrently? Separately, is there a specific image that is larger that perhaps is the rate determining step?
Note that URL support won't solve the performance issue. It will only make it more convenient to pass URLs to fetch images instead of needing to create URIs with base64Data in your application.
Separately, when you say you will load 200 images later - is this all in one card collection view, or something that you would want to paginate on? If you're loading 400kb * 200 images = 80Mb of images, that feels like a lot of data to block loading on a mobile application. Could you also share more about what you tried when you said pageination also does not change the runtime?