New to iPhone. Can some iOS experts

I got my first iPhone, the iPhone 7 over six months ago when it first came out. For the most part, I love it and I love iOS; I don't see myself switching back to Android specially when I got to learn how iPhone backups using iCloud and iTunes are much easier than backing up a Droid for example. People I know that use iPhones have told me that iCloud and iTunes are very similar in terms of functionality but iTunes is a bit more comprehensive and faster due to the fact that it doesn't have to download your backup from the cloud which can take some time. I was wondering though, can I solely rely on iCloud backups? Because I find it easier and more convenient than having to plug in my iPhone to Mac or PC. Also, how secure is my iPhone with a passcode lock? Let's say it gets stolen, can an expert unlock it and retrieve all my data, or at least erase my data and use my phone like a new one? Can I erase everything off my iPhone while it's missing but still have everything on the cloud?

Yes, you can trust iCloud backups.

Yes, you can trust 'local' backups.

The encrypted backup version is slightly better as it can then backup passwords, etc.

Your phone is very secure with passcodes, VERY difficult to break into.

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So, here's the advantage of iCloud backups:
Let's say you are travrling and your phone bricks. You go to the Apple store and they reset it, or give you a new phone.
>> If you don't have your pc, you'll need to wait until you reconnect to restore.
>> If you have the iCloud backup, you can restore while in the store. You walk out fully functional.

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