Have you tried Clearing the Chache on your Google Play services?
1. Go to Settings
2. Apps & Notifications
3. Google Play Services
5. Clear Chache
Also Ive seen people have this issue because Auto Sync is turned on in the backgroung and is running the battery down.
2.Account Sync - You can see wheather one or more of your accounts are syncing.
3. Sync On/Off
You can try removing the notifications from it.
Although, your active 2 should still hold a lot of your battery.
Those percentages just get distributed within the apps you use the most. Doesnt necessarily mean the calender app itself did all the damage. It just means that out of all the apps. That one used the most. Keep in mind that percentage doesn't include the whole watch system usage of the battery