You've always been able to side load apps you are correct.
However, this is not what Google wants. Over the years, Google has started to enforce more restrictions on third-party applications. They've been slowly making these options more difficult to find in the settings of certain OEMs. Just because they give you the freedom, doesn't always mean they care.
But yes you are correct that Apples monopoly on their app store is way worse. But Google would absolutely remove more user choice settings if certain things like the GPL didn't stand in the way of the Android OS.
If Android had never been open-sourced, they would absolutely not have any options for third party installations mark my words.
They only thing standing in their way is Linux and the GPL.
Google is just as malicious as Apple. They are just better at hiding it.
Personally, it's not Google's place to dictate how an app verification ecosystem works. If a company has developed an app, they need to be the ones to make sure it's secure in the first place, not trusting a monopolist tech company that has almost all control with how someone uses their phone.
Google has rules yes, but Android is open-source and should be open with a free & open market for apps. After all, we paid for the device.