EBS optimized VMs looks nice on paper, you can choose the size and pay for your needs only. But the once you start to use the disk in production you see the problems.
In short, if you want to use the disk a lot, you need to pay a lot. If your app is slow on aws and uses EBS as storage, increase the disk size, not the VM instance type. This is true mostly for database performance, which once the RAM is filled, relies on IO a lot to get new pages from disk.
This is the kind of advice I wish was easier to get. The AWS docs are very lacking in my opinion for "If you're exhibiting this specific performance problem the cheapest option is to increase [x]" where [x] is increase instance size, disk size, performance, add a read replica, etc...
In short, if you want to use the disk a lot, you need to pay a lot. If your app is slow on aws and uses EBS as storage, increase the disk size, not the VM instance type. This is true mostly for database performance, which once the RAM is filled, relies on IO a lot to get new pages from disk.