What you should be more uncomfortable with is the fact that there's basically no way to exfiltrate that data in any cost-effective, practical manner and there's zero recourse if a backup storage company goes "oops" and loses all your data or one day decides to just close up shop.
I don't think backblaze has a chance at losing data, but I really use it as the last resort "oh shit" place. If I lose a drive I'll pay a bit of a premium for whatever multiple of 8TB needs to be sent my way, I'm going to be replacing a $2-300 drive anyways.