why TMobile home internet so bad

I was chatting with Tmobile (again) several days ago, about one of the other issues I have had with them.  I had given up commenting on their home internet, and then he said "is there anything else..." so I mentioned it with low expectations  ( expected reboot devices, move my gateway, etc…I knew it was not on my end  - having been a network engineer for several years).

He mentioned about sending new hardware and I declined.  He then mentioned something about refreshing their network settings on their end.  I did have to reboot the gateway, but after they did something on their end, they said it would take 24 for 48 hours to take full effect (odd, but OK)

It has been a few days past the 48 hours and it has been good, but too early to say it is reliable.  I have a speed test app on my phone so I have a easy way to track the history of my bandwidth and ping.
 A week ago, when I had trouble streaming at 4:45 pm (before the refresh), I was getting 35.5 Mbps download, which can barely support streaming at 4k quality.  Usually I get 250+Mbps which is way more than needed.

Time will tell if the fix on their end will fix it.