At what scale have you found Performance and Size Limitations an issue? I've seen people leave due to cost before (not that I thought they were always correct), but not for the other two you listed.
30,000 iops is 1/2 of a crappy consumer grade SSD.
6TB is fairly low for projects that generate any sizable amount of data.
We don't run things in AWS unless it's strong client preference.
Not to mention 30k IOPS and 6TB is very expensive.
You're looking at $2700/mo for the IO provisioning and $750/mo for the 6TB of storage. Double those if you want Multi-AZ. Then you get to price the server size which I imagine is one of the more expensive options if you need 30k/6TB.