You are replying to a post which is two years old, and a lot has changed in that time, so people may feel a little confused. 
As far as specificsā¦
While lighting groups are not available in ST,
As of this writing, smartthings does offer lighting groups, itās just that you canāt do anything with them except activate them through the smartthings app. You canāt include them in scenes or routines and they are not visible to the voice assistants. 
they ARE available in Amazonās Alexa app which integrates with smartthings and acts as a controlling front-end for ST so Iād recommend you install the Alexa app for this use case. Of course the Alexa app will provide plenty of other ST features such as voice control, new ways to design if>then commands, etc, and you donāt even need to own an Alexa device
The smartthings integration with Alexa is complicated. Alexaās groups are great, but they are NOT available for use in SmartThings routines. You can use them in an Alexa routine, but then you are back to needing a virtual device to trigger that routine from SmartThings. So great for voice control of a group, but otherwise does not meet the OPās requirements. (At the time the original post was written, āautomationsā was the term used for what are now called āroutinesā in the smartthings app. So that was a very specific question not related to voice control.)
The problem with using virtual switches to control groups of lights is that they remember their āstateā. i.e. if you turn all your lights on with the virtual switch and have your physical switches mirror this, it will work great. But then if you use your physical or any other kind of command to turn the lights off individually, the next time you tell ST to turn on the virtual switch it will do nothing because within ST the switch is already on; as it was never turned off.
SmartThings has always offered several different types of virtual devices. There are both virtual binary switches, which are on/off devices, and virtual momentary switches, which are more like a doorbell button. You turn it on and then it immediately turns itself off again. Its resting state is neutral. So the issue you raised will not be a problem as long as you use the right kind of virtual device. 
It is definitely strange that two years later smartthings lighting groups still are not actionable except in the app itself and still donāt work with the voice assistants, but there we are.