I live in Pennsylvania and travel to Connecticut and West Virginia all the time. I don't see coverage issues and in fact in the back woods of the country Sprint has better coverage due to a few acquisitions it has made in that area.
TMobile has a real problem on the East Coast. Coverage is bad in my city. Doesn't work in WV and when my son was sick with cancer CHOP (Children's Hospital of Philadelphia) in the Surgery Wait Room they tell you that they can't call you if you have TMobile, which means you can't leave the waiting area at all.
In other words, Sprint's coverage is great right up to the moment when it's terrible. Which you can live with if you're mostly in a place where it's great, but which makes it hard to recommend to people generally since you have no idea if they happen to spend most of their time in places where it isn't.
Sitting in my home office, my work-provided Sprint iPhone 6S just managed 0.47/0.27 Mb/s in the Speedtest.net app. Highest I've ever seen is 13.11/8.85 in Highlands, NC of all places. Data dead zones are everywhere around Atlanta.
Sprint is so bad that several times a month I can't even get it to make a phone call... over WiFi.
My Verizon iPhone 7+ got 38.25/9.25 with a best of 172.92/29.85.
Except it's Sprint, so many people will whip out their phone and have no functional data service. (Yes, even in 2017). There are lots of really good reasons why Sprint has the worst reputation of all major carriers. And people don't always pick up on the distinction -- a broken network makes a great phone look like a broken phone.
I think Essential is letting their business/personal ties to SoftBank cloud their decisions on what's best for their users and what's best for Essential as a product.