Google calendar is actually terrible for people with focus problems. Or at least I haven't found a good way to manage its alerts in a helpful way.
For one, basically all alerts are the same. Meaning there's no good way to make noisy alerts for critical events and quiet ones for mundane things. You can set multiple alerts for an event, like 1 week before, 1 day before, etc. But it's manual every time.
Something more like PagerDuty style alerts that let you set up classes of alert patterns would help. Alerts that blow up your phone until you get them would help. It's so easy to have the calendar alerts go completely unnoticed with just a chime if your phone is in your pocket or in another room or if your alert volumes don't happen to be perfect, which is pretty much impossible since background noise levels change throughout the day.
Even such minor things, like when you snooze an alert and you can configure it to notify X minutes before the event, if you select 0 minutes it still alerts the minute before the event which is enough time for me to get distracted again.
No, it's one of my biggest disappointments of technology today is that such basic tools are so poor at their job and lack such straightforward configuration controls. The tools are made to work for Google, not for you.
So of course people are going to points loads of third party add ons, and hacks to get calendar to be marginally more useful, but WHY should we need to jump through hoops to make our devices serve some actual useful purpose for us?