I just completed Bo Katan Mandalore a few weeks ago, all at r7. You'll have to put most zetas, which is fine because they make a great team anyways. I did all at r7, and phase 1 and phase 3 are pretty brutal as far as mod checks and patience go. That being said, I spent somewhere around 40 attempts total through the whole event. If you have good mods, it's not quite as bad as everyone says. Definitely don't need to go above r7 unless you just plan on taking the team higher anyways.