The best way to manage calendars in Gnome is Evolution at the moment. Gnome calendar is pretty and all but it lacks a lot of features, just like you described. Even simple things like adding attendees to calendar events in google calendars or timezone-awareness which you also mentioned.
Evolution integrates with Online Accounts, which Thunderbird does not. And therefore it integrates with your notification area. The one thing it doesn’t do for me is to detect online meeting links and offer a button in response (like you would see on calendar events directly at google calendar’s site).