Yes. These are all very accurate observations. I'm an Alexa and Google Home household, so I have Google Home playing MP3 sounds when someone rings my doorbell (but I do hate that startup sound after the 5 minutes of inactivity), and Alexa does TTS for me. We listen to all our music on the Echos and they can do TTS and then continues the music perfectly.
There's different methods for TTS with Alexa. All need some kind of external server running I think, which is fine with me. We're not talking a big computer here, just an old laptop (which is what I use) or a Raspberry Pi. The method I use utilizes Google Assistant Relay and SmartThings, not to be confused with having any reliance, or need for Google Home or a SmartThings hub. You don't have to have ever owned either of these. What I like about it is, this method works for Alexa TTS and it gives me an awesome tool to control anything from HE that Google Assistant can control.
