You're talking about your connection, that's not a cloud problem exactly, but it is related.
RAR is a really old format, and by combining files you increase your risk, as one compressed archive corrupting takes out a lot more files. It also won't help much as images are typically highly compressed already.
I use 'store' no compression for photos.
I get your point about a single file corrupted will mess up whole thing; however, I have many other backups, and also splitting and encrypting folders assures me my files wont be seen nor stolen by anyone.