Is it "safe"? It depends. How strong is the password? I would say that storing multiple copies of your data weakens your protection. If it's the same password on 2 different locations, an attacker has 2 possible places to find your data, not 1. So the obscurity factor (not a good way to provide security, but nonetheless has some value) is reduced. If you use the same password, they'll need to crack it wherever. Now say you have 2 different passwords, on 2 different storage places. You're correct in that the level of protection is as good as your weakest password. Now think of this: identical data is stored in 2 places, and an attacker now doesn't need to guess 1 and only one password, they have to guess 1 of 2 passwords. That, to me, doubles the possibilities of finding your data. I'd only store my data in multiple places for availability of the data or disaster recovery - not security.
From a security perspective, a more effective way to protect it is with a 15-character password. That will take a long time to brute-force, especially if you add special characters or Alt (non-English) codes for a character, such as ä. (Alt+0228)
If you really want to secure your data, there are services that offer what is essentially RAID over multiple cloud providers. So they crack your data on Amazon - big deal. Without cracking Azure and Dropbox, they really don't have much to go on.