You didn't answer my questions, so it's difficult for me to give you my perspective. This isn't the same for others, and it won't be the same for you, but I used IB+BB until level 120, then I used mostly IB until 135. After that, I switched to DB. I used Clashing Spiral when I was still level 99 to do most of the Eden Group 91-99 quests, and I used Clashing Spiral for some of the 100-110 quests.
Clashing Spiral is a single-unit attack.
IB and BB attack multiple units. You can choose to level by attacking single units, but it's much faster to mob. Ignition Break also does more damage if your weapon is endowed with fire element (from weapon, scroll, or spell).
If you prioritize survivability, do you plan on wearing leeching equipment? Examples: Rideword Hat, Vanargand Helm, 3x Hunter Fly-carded RTE, Thanatos weapon. What's your preference when it comes to using healing items?
The problem with Hunting Spear for a Rune Knight is that Hundred Spears does more damage than Clashing Spiral, but HS does more damage with a lighter weapon. You can combo CS after HS, but I find that it and autocast Spear Boomerang get in the way if I need to cast Spell Breaker on a boss. If you have a Royal Guard, your investment in Hunting Spear makes better sense until you can get Imperial Spear.
