Well, it is generally more likely to be tuned to AWS, containing right drivers and tools installed than a default distro you would download from the website, but the images that are available on AWS would likely also tuned similarly. If there are some issues where other image is noticeable worse they would look into AmazonLinux and apply the changes from it.

I would say that AmazonLinux is likely to have less issues with latest instance types (if they change something "hardware" wise, for example when AWS started exposing EBS using NVMe drivers there were some issues originally).