Meaning total trust with your cloud provider / app manufacturer. That is your choice, I wouldn't do it. Selfhosting is kind of a pain still, but gets easier every year (and for simple file sync that you mention, it's already rather easy).

If syncing is through iCloud, you'd only have to trust Apple and nobody else, if I understand things right. And yes, I trust Apple a thousand times than I'd trust a web hosting company or all the open source projects involved in self hosting.

Self hosting is an unsurpassable mountain for 99% of people who need to use computers. The risk to security and data loss is much higher than from syncing your apps through iCloud or through the app manufacturer.