+1 for Backblaze.
I finally gave up on Time Machine, even with a direct attached drive, and switched to Arq. It backs up to a NAS share, and I've configured it for a similar tiered approach as Time Machine. Hourly backups, with the last 24 retained, and the last thirty daily, last fifty two weekly, etc. The Arq backups perform significantly better, and even take up less space than the equivalent Time Machine ones did.
For me, having a bootable backup isn't important. If my machine died unexpectedly, my process for getting back up and running would be to restore my home directory to a different machine, install the most important apps first, and go from there.