Your link's math says that SpaceX is marginally profitable selling 220GB of internet at $50 per month using 2016 bandwidth levels, which is pretty impressive.
Those numbers are from the original 2016 FCC filing, they've got a lot more bandwidth out of the satellites now because 4 years is a long time in technology. Musk says 3Tbps per set of 60 satellites. That's 50gigabits per satellite, not 20. Shotwell has indicated a price of $80 a month, not $50. And you know that's going to be the low price, not the high one. So let's assume that includes a 100 gigabyte cap, which is still about 10X as much as you get with the base plans from the geostationary satellite providers.
Those new numbers increase the subscribers per satellite from 7000 to 38000. Revenue per satellite per month jumps from $35K to $300K. At 60 satellites per launch over a lifetime of 5 years, that's gross revenue of $1.1B per launch.
Re: your other point about latency. They've already got 28 base stations in the US. That's enough to cover the continental US without any hops.
To be more explicit, before they sell you service at a location, they will ensure that they have enough base stations close to you that both your terminal and a base station are both always visible to a single satellite. The base station is connected to an internet backbone. So the signal goes from you to the satellite to the base station to the internet backbone. The reply goes in reverse.
So yes, this means that they need to have a similar number of base stations as satellites in a minimal constellation. They've said that a minimal constellation for full US coverage is 1000 - 2000. They have 28 base stations in the continental US, 2% of the globe's area. Yup, 28 is about 2% of 1000 - 2000.
The cost will need to be very expensive, relatively speaking. See this quick math for why: https://mobile.twitter.com/quirkyllama/status/12727488943806...