When comparing Sigfox to LoRa, they are not even that bad in terms of openness:
The Sigfox protocol specifications are public:
https://build.sigfox.com/sigfox-device-radio-specifications
This is in contrast to LoRa, which remains a closed protocol (I am not talking about LoRaWAN, that part of the spec is open, but LoRa, i.e. the physical layer stuff).
So there really is a tradeoff here:
If you want an open wireless protocol compatible with many standard RF transceivers, but a proprietary backend and device library, go for Sigfox.
If you want a closed, proprietary wireless protocol that only works with Semtech chips, but an open backend, go for LoRa/LoRaWAN.