Home Assistant isn't "yet another" service. It's not trying to do vendor lock in: you can think of Home Assistant kinda like a "glue" framework.
It's meant to let you systemically attach devices/software across any number of mediums, and pre-existing services, and let them play nice.
So if you've already gone and set up your Google Home, or Alexa, or Apple Homekit, you don't have to abandon them to use Home Assistant.
Sometimes you can't even get away from it: the thermostat that came with our rental basically only has a useful Samsung Smartthings integration, but we can still use it with Home Assistant.