Then don't look at the sponsored speed test. There are many others. And yes it does vary by city. But looking historically you'll also see them climbing and surpassing others. With the low frequency rollout and more phones to support it they should dominate everyone easily.
T-Mobile is last in line on exploring 5G. AT&T is already testing in many cities, with Verizon starting next year along with Sprint. T-Mobile has no plans to do so in 2018. They continue to be behind.