I’m not saying you shouldn’t back up applications; I’m just saying that in my experience it’s not a big win in a tertiary backup for most people for the reasons I stated.
I don’t want someone who hasn’t thought their individual situation through carefully to get hung up on “Backblaze doesn’t back up applications” as a problem, because it’s not in nearly all cases. Configuration files, preferences, licenses, and so on are almost always stored in ~/Library so downloading new copies of apps doesn’t require any more setup than switching to a new drive would.
So yes, if you store data in /Applications (don’t do that), rely on programs that cannot be downloaded ever again because the company is defunct (store a DMG of the installer elsewhere), or the like, not backing up the Applications folder could be problematic in the event of a catastrophic disaster that destroys your primary and secondary backups as well.
In that case, you’d want an offsite backup service that lets you back up absolutely everything,