The net result is that after waiting for 3 years for this to happen the only way to get true calendar sync functionality is to pay a 3rd party $120 per year.

Really? 

I confess that I do not understand why the ZCRM team could not solve this on their own. Now you want your users to grant a third party access to our accounts and increase the exposure for security breaches. On top of that we have to pay someone else for that "privilege". The professional subscription is $15 per person. Keeping my calendar synchronized across devices will cost me an additional 2/3 of that monthly subscription.

I strongly encourage the ZCRM to find a way to do this themselves. I can see charging a nominal fee to cover the costs of keeping up with ever-changing Google protocols and policies. But to fob this off on another party and then make it more complicated for your users is NOT a smart plan. 

From a customer's standpoint if I have to start using other cloud based services to make ZCRM work properly I now have more control/access points to worry about for security and performance. I might as well start with a blank slate and start looking at an all-in-one solution that can accomplish what I need.