I doubt it's a question of data control. EC2 is significantly more expensive than running your own servers so it's a good idea to keep close to your base load

I doubt it's a question of data control. EC2 is significantly more expensive than running your own servers so it's a good idea to keep close to your base load on your own servers and then just scale up/down as necessary with EC2. This way you're optimizing your cost per player.