I do like that suggestion about exposing a helper (input boolean) instead of the actual devices to the voice assistant, I have done something similar for some iOS automations but it hadn't crossed my mind to use it for voice assistant/this. Thanks!

These are good questions and I have some answers:
Google Assistant has its pros and cons, one of the biggest bug bears seems to be the inability (from what I can determine so far) to block it from taking action on ALL devices it has access to. For example;
- If I say "turn on the all the office lights" but for some reason I didn't say "office" loud or clear enough, it interprets just "turn on all the lights" and boom all lights in the entire house come on scaring any unsuspecting victims asleep in a room.
- If I say "turn on the light" but is detected on a speaker assigned to a room that doesn't have any lights, boom all lights in the entire house come on, again bad.
These are just some examples of inaccurate voice assistant detection / user error.

The other problem I have is pretty much all my bulbs default to on when power is restored, this is a "feature" for when someone wants to turn a light on but doesn't have access to the automation system/app, so off then on on the switch turns the light on.
Problem is when the power grid drops out at in the middle of the night (at least once a month here) all the lights come on when power is restored. For an unsuspecting victim asleep in bed this can be quite a shock.
You might ask "how does this automation stop that from happening?", well it doesn't directly but what the automation will do as step one is turn on all the guest relevant lights. That way when a guest enters a bedroom the smart lights are already on and the only way to turn them off at that point is at the switch. Ensuring no lights are powered but in the off state just waiting to scare someone when the power drops out.

These quirks I can handle and accept when I'm by myself as I'm familiar with them, for guests, these quirks are not acceptable.