All it's telling me is the amount of speed that the network is capable of. Not the amount of speed I can receive, which is more important.
For instance, Comcast can give me 100 mbps at the flick of a switch, but instead gives me 6 mbps, what I'm throttled down to due to my plan. Sure the network is capable of 100 mbps+ instantly, but I don't receive that. By tmobile doing this, it's almost as if Comcast lifts off speed test so it'll say I receive 100, 200, 300 mbps when in actuality I only receive 6 mbps.
The data speeds I receive are more important than the "theoretical" data speeds the network is capable of.
Even when tmobile throttles you back, it's not web browsing that's going to be slow. In my experiences after being throttled, the only thing that can't be used are video chatting apps and watching videos. Everything else works except those two data hogs.