A limiting factor is Siri. It took them 8 years to allow asking to play a particular song on Spotify.
Usually the first thing I say to Siri is 'Hey Google' so it goes to Google Assistant.
I'm not really sure what "seamless integration" is left. I (and my friends that have similar devices) use smart speakers for power control, getting the weather, playing music, and setting timers/alarms. It doesn't take an sole-source ecosystem to make that work well.
