OK. I checked and don't understand why it is not overriden.
Lets fix it by the other way.
Do not show map by component (menu item).
Just create Custom HTML module, enable plugin processing, publish it in where you want to see map, and in HTML body call my plugin.
And for map in Advanced options set "CSS Class" to any your name, it is map div CSS class.
In that case, due to you write CSS class - I ddn't use default CSS class name. And for plugin map div will be not "GMapsID", it will be the other.
In result - my CSS styles will not be applied to main map div. And you'll not get my override max-width: none
Try to do like this.