To me a big part of computer science is abstracting away unreliable details to make them seem reliable.
Now of course that assumes they are uncorrelated, but since Sia nodes are distributed across the internet, that's likely as opposed to multiple servers at a few data centers like AWS.
Turns out mortgage bonds tend to be correlated.
Tying two bricks together doesn't make them float.
It is when you just start bundling everything and then saying the entire thing is AAA that the trouble starts.
Talking about the disk-space pricing is, IMO, disingenuous. Talk about the math for an all-in use-case of the service. I appreciate what the OP is going for, however, hand-waving around uncomfortable critical items like bandwidth cost for the Sia network is not a good look.
You really need to back that math up.
Here's my math: 10mbps is over 3TB per month at max utilization, so let's say it's good enough for either 2TB throughput with semi-even use, or 1TB throughput if the use is really focused on part of the day.
When buying transit in bulk in the US, Google tells me that 10mbps was very roughly $8.50 a month in 2017, $4.50 a month in 2018, and $2.50 a month in 2019.
Are you expecting the data to be rebuilt every single day or something?