I've inadvertently turned off lights and AC's at my other property while it was rented out to Airbnb guests lol 
they thought the property had a poltergeist
It does partially solve the problem. If you have alexa set up with room groups, like you said, and the echo device you're speaking to is included in that group, you do not need to mention the group name at all.
i.e. if i'm in the living room, speaking to the living room echo, and say "alexa, turn lights on", it'll only turn on the lights in this room. I didn't have to say "turn living room lights on" and introduce ambiguity.
Yeah, same with Google Home (GH). But what if you have Alexa on your phone and it responds (rather than the echo device). Which target device gets activated then? This is the problem with Google Assistant (GA). It isn't linked to a home or a room. So it could end up activating a device at another property (which is fine if that's what you want to do, but I do feel they should include an option to have GA aware of its location and work accordingly, like GH). So when the GA device is connected to the WiFi of the home, it should operate like a GH device in terms of addressing the local devices in my opinion.
That's true, I forgot about that other part of your issue. I guess I'm lucky that my OnePlus phone doesn't respond to voice cues when the screen is off 
Edit: what does the Google assistant on your phone do if you just tell it "turn lights on"? does it turn on all the lights everywhere? Or does it prompt for clarification like alexa does on occasion when the request is ambiguous? Like, sitting in the room with your GH, and whisper to your phone so that only GA can hear you?
I'm really careful what I say nowadays anywhere near my phone 
Actually the other day I asked one of my Nest displays to turn off or on something (can't remember the details) and I saw my phone screen light up and displayed the GA, but the GH device did the response and managed the action. So I'm wondering if it's now smart enough to default to the GH device if multiple GH/GA devices are triggered. If so then that's really helpful. Or maybe the GH device was just nearer or caught the command better. I didn't explore it further to be honest because I normally just talk to the GH device when I want something done in the house. Well, or my wife lol.
Multiple vs Single accounts in Multiple locations question.
My Smartthings v1 hubs are obsolete and will be replaced with Hubitat C7 hubs.
I have 2 separate locations.
I have mainly Z-wave devices (older GE switches that need polling), a few Zig-bee bulbs and sensors(50-75 devices in one location and 75-100 devices in the other) and a few 3rd party cloud based devices in both locations.
My family uses Google Home's voice commands as their primary means of interacting with the devices.
I already have one Hubitat C7 hub and Google Home account setup and associated with one location and am trying to decide if I should keep the same Google Home and Hubitat accounts and just add the new location to the Google Home and new Hubitat hub to the Hubitat account or setup 2 more accounts to prevent any issues with Google Home confusing the voice commands to devices with the same name(kitchen lights) in different locations on different hubs. This was an issue with Google Home and Smartthings and I ended up with 4 accounts (2GH and 2ST) to prevent any voice command issues. Google Home can now separate homes but I have not tested it out and was hoping to get some feedback from people who have already dealt with the issue. I dealt with the Google Assistant on my phone by having Tasker turn Assistant off when I connect to the location WiFi. You can also switch the Google assistant account to match the location account but it is more complicated and requires root.
So my options are:
4 accounts:
GH1-HE1>Location 1
GH2-HE2>Location 2
3 accounts:
GH1-HE1>Location1
GH1-HE2>Location2
or
HE1-GH1>Location1
HE1-GH2>Location2
2 accounts:
GH1-HE1>Location 1&2
I know I am not the first person with this type of setup and have seen some other posts regarding pitfalls of Hubitat with Google Home but have not found any specific information related to accounts setup pros and cons.
