Behind the tiers of soldier species, it is actually a disparity in technology.
It's like how World War I cannons couldn't hit World War II planes, let alone intercontinental missiles.
A level 90, five-template boss should be a devastating force against lower-tier soldier species.
After all, dealing with such an existence involves mobilizing interstellar fleets, Tier 3 Civilization Architecture, and Star Defense Systems.
This is also the usual tactic employed by low-level civilizations when confronting Tier 3, or even Tier 4 and 5 powerhouses.
Relying solely on soldier species is actually a very inefficient and largely useless approach.
This is why the Walter Clan's senior members unanimously agreed to the beheading strategy, because ordinary interstellar influences simply cannot have as many Tier 3 powerhouses as they do; having even one or two is commendable.
