It's only simple to you because you don't understand the nuances on which these issues will be argued.
The FTC will argue things such as:
1. AT&T is too large for certain types of consumer hostile language or practices to be reasonable in their contracts.
2. The primary marketing and representation of the unlimited plan to customers substantially contradicts the subsequent practices implemented by AT&T and any of the fine print in the contracts.
3. The congestion control placed on unlimited customers was purely profit seeking and not based on any sort of necessity.
etc. etc.
You think at&t's language in the contract gives them an out on this. It does not.
Congestion or not, they aren't required by law to provide you with unlimited data at a certain speed period. The only consumers I believe have been wronged are those who were currently in a contract when the throttling had started. Going into the contract, that wasn't spelled out, even if at&t's verbiage protects them in situations like this. When you resign your contract, you are effectively agreeing to new terms and conditions, even if that means throttling of your unlimited data.