There’s no elegant way to do it, but you can do it.
If you want to do it without using any custom code at all, use smart lighting and have all of the lights in the group except one follow the one you left out. That way it becomes the master switch and all of the others will go on or off as it Does.
If you’re willing to add a virtual switch, then you make the virtual switch the master and have whatever combination of other lights you want follow the virtual switch. That way you still have individual control over every switch. You can also use multiple virtual switches and have each one represent a particular grouping.
This method is straightforward, even if it’s not intuitive.
One caveat is that SmartThings at present will only allow you to have 100 devices of “capability.switch” so don’t go too crazy with virtual switches or you’ll run out of slots. 