[VoiceOps] VoLTE vs UMA (GAN)

Good day, would it be valid to compare VoLTE vs UMA/GAN, and if so what would be the differences? My 10,000 feet view is that UMA/GAN is an older techology for switching voice between WiFi data channel and an actual GSM/3G voice channel. Whereas VoLTE is a fairly recent spec and it switches between WiFi and LTE, both being IP data channels, sort of like your 'eth0' and 'eth1'. I guess both integrate heavily into core mobile network and into headset OS, and would offer similar user experience? Both can be leveraged by either MNO or MVNO, but not by some sort of over-the-top app? Many thanks! -Victor