Looks like Selectdude in another thread said it happens all the time in Chicago

I can confirm that an MVNO I was using in Tokyo barely worked during rush hour. It was like a 2g connection or worse

If I have to guess, congestion can’t be just about the total bandwidth being used. It has to also do with the number of connections to a tower. So any densely populated areas will likely be perennially “congested”.

As an mvno user I do occasionally see it. My wife and I will both independently notice that our data has been garbage that day.

Another person here chiming in with my experiences, I see it a good bit but it is not as bad as one might think most of the time.

If I do a speed test in the city square near me late at night, I'll easily pull >100Mbit on my phone. Utilization at like 3:00 AM is next to nothing. All the bars closed over an hour ago, there's nobody out and about but me coming home from a late night datacenter run.

I go to the same public square at 3:00 PM and I'll likely get 10-20Mbit. More than enough for most things I need, but definitely nowhere near what I was pulling at 3:00 AM. Friends with T-Mobile postpaid plans with me will probably still be able to pull ~100Mbit.

At big crowd events especially in places where there aren't usually as big of crowds (balloon festival, airshow, etc.) connections can be anywhere from okay to next to worthless. Maybe I'll get a megabit, but chances are even Signal might have to retry every now and then to send a text message.

Does everyones speed decrease like that or only MVNO?

I've definitely experienced big crowd events where friends with me on T-Mobile on similar generation phones had plenty of network performance available to even stream video while my phone on Mint could barely load a webpage.

I use Mint in the Bay Area and I’m quite happy with it. Just paid for my second year. I generally don’t perceive much deprioritization. I notice it when I’m streaming music and I hit the Bay Bridge toll plaza with a bunch of traffic (or that’s my assumption, at least). Other than that and maybe a very crowded airport, I can’t think of any other cases.

My wife and I have had Mint for 3 years in NYC and I don’t recall ever having had a situation where there was good service but slow data. Speed tests on 5G generally run over 400mbps.

I did a trial before we switched from a regular AT&T plan and I had significantly faster internet at my office, on the subway, and at home than with AT&T. The AT&T service was typically useless at sports games and concerts and stuff anyway, so the concept of deprioritization didn’t really phase me. Saved us $1000/year and we got better service. Couldn’t be happier.