I think a lot of people are attributing speeds of 200-700Mbps to mm wave when it's actually pretty ordinary speeds for 2.5-5GHz coverage today now that carriers have decent capacity there. If you're getting below 144Mbps, you're in the bottom 25% of T-Mobile's network experience. Over the past 6 years, speeds have gotten a ton faster, mostly from 2.5-5GHz spectrum. Verizon is the only carrier that put much effort into mm wave and it still covers basically nothing.
Ignoring latency, you're likely to get speeds similar to wifi from today's mobile networks without mm wave - unless you have a really great home internet connection and a good wifi setup. I have a MacBook Pro, but it only has wifi 6 and I can get 700-800Mbps out of my wifi, but I'm not getting 2Gbps from it.
How is it a better deal to spend more money for essentially the same thing?
Imagine you're buying food that will go bad tomorrow. You can't keep it. You can't share it. You can buy enough food to fill you up today for $5, or enough food to fill you up 50x for $20. You will still eat that one unit of food, the other 49 units will just go to waste. Which do you buy?
For all the time I've had Mint, I've saved nearly $3,000 compared to your $50/mo plan. I've never felt the urge to really need more data personally, and it's worked well for me on my international travels around North America. If the outcome was the same, wouldn't you rather keep $3k in your pocket?