Current SC's prices are good for renters, but not the hosts.
Simple math tells us that with a 15 TB hdd farm, I'd make 4.5 usd/month by renting all of those disks. That's based on your very own numbers.
It's not even worth the electricity.
Sia will never be a good hosting solution, it's either unprofitable for the renter or the host.
You point out exactly why Sia has an excellent chance of becoming the premier storage provider. Hosts are currently accepting low rates as overall demand is low. One only has to look at the jump in contracts to see the low rates having the expected impact (
https://siastats.info/index.html). When the system matures and we reach an equilibrium of sorts, prices will rise. No person is mandated to accept prices in a free market deal. Any agreed upon deal can be accepted as beneficial to both parties; else, there would be no contract. To the best of my knowledge, Sia is the only game in town that has created a true decentralized free market. Free markets are the most efficient in the world. If the devs stay on this project til maturity, Sia may very well become a game changer. Kudos to the hard working coders.