yes, for new customers, unlimited-throttling is better than flat+overages, but it is not as good as unlimited (which is no longer offered). the problem, as you pointed out, is that at&t baited & switched.
and to be sure, throttling is a limit. for those on unlimited plans and according to the way it was advertised, you should be able to get up to the physical limit of the network every month. if that's 500GB/month, the you should be able to use 500GB/month every month according to the agreement. allowing you to use 5GB at the normal rate and 5GB more (or whatever it is) at a drastically reduced rate is not unlimited. the fact that they didn't consider bandwidth requirements when they made the offer is not the concern of the customer who accepted that offer.
and to be sure, throttling is a limit. for those on unlimited plans and according to the way it was advertised, you should be able to get up to the physical limit of the network every month. if that's 500GB/month, the you should be able to use 500GB/month every month according to the agreement. allowing you to use 5GB at the normal rate and 5GB more (or whatever it is) at a drastically reduced rate is not unlimited. the fact that they didn't consider bandwidth requirements when they made the offer is not the concern of the customer who accepted that offer.