But the calculation is harder than that. People are terrible at estimating the ops personnel cost for DIY. Turns out it's hard running with minimal downtime, or engineering hardware + software to be fault-tolerant. It's hard to put a price on dev tools/APIs/doco/the whole eco-system.
Especially for that last reason, I have never been "blown away" by Softlayer, even when their instances were way beefier than anything AWS/GCP offered. YMMV.