Yes normally bigger is better when you're doing graphics work but it's overkill for a profile, especially for smartphone users. Having said that, I do agree this can be improved and will look into bolstering the image processor to accommodate images larger than 5000 x 5000 pixels so it will resize it automatically for you.
Until it's ready, as a workaround you should scale your image down to ~1920 pixels in width using a graphic editing application (e.g. Photoshop) or if you don't have one you can use this online tool:
http://www.picresize.com