You've got that impression entirely wrong.
SmartThings is the most open platform on the market at this moment, not counting extremely minor players and unreleased products (er, WigWag...?).
Nearly any Z-Wave Device is instantly compatible or addressed by http://community.smartthings.com
I was also able to load up my home on a budget with Best Buy PEQ branded ZigBee open home alliance compatible sensors and outlets when they had a half-price sale. Nothing "proprietary" there.
There have also been more successes than failures in getting IP and Cloud-to-Cloud Devices working... Including official and unofficial Amazon Echo integration.
The automation / coding complexity (and other UI shortfalls) are ongoing... But, again, the Platform is open enough that there are no less than 2 "Rules Engines" (and several free "SmartApps" published by the Community that, I believe, handle your fan use case easily.