That is my thought on all of the ‘cloud’ options. The company writes the software that does the encryption and there is noway to know if there is a backdoor to the system.
I just purchase a Synology 2 disk NAS. It is running at RAID 1 and allows me to access my data from anywhere in world thorough my laptop or my Android phone using HTTPS. True if the house burns down I would lose the data on the disk, but all of the important stuff is on DVD backup anyway and kept in a fireproof safe in the basement.
My data is never going to be out in the clouds.