Good point.
Assuming both Apple and iMazing are not malicious (most likely scenario):
(1) With iMazing or a similar software I can do all this offline and/or local, I do not need to upload my data to a server.
(2) With Apple, my data are on their servers for sure where they are possibly stored forever and used somewhen by whoever as Apple has to consent to the local laws and authorities. Just think of the iCloud in China where the government seems to have all the access (almost certain). I am no sure this is much different on Apple's other serve farms.
Should iMazing be a malicious software, they still don't have the data if I do the backup and restore on a offline machine, which is actually my plan.
Clearly, the best solution would be an open source iMazing (assuming it works as advertised), or at least an Apple that does its job and delivers a proper backup and restore software with every iPhone, separated from a music and movie store. Conceptually, iTunes is arguably the worst piece of software from Apple, in my opinion.