Your numbers are skewed, because Nighthold is not a linear instance after the first 3 bosses; you have the choice of going to any of 5 different bosses next. Therefore, obviously a decent percentage of guilds reaching 3/10 are choosing to go to one of the other bosses first. It's a faulty assumption to classify a guild that is 3/10 and working on Krosus or that killed Krosus and is 4/10 and working on Botanist as "stuck on Spellblade.
Guilds that are stuck on Elisande or Gui'dan are a larger percentage in all reality than on Spellblade.
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Again, 100% irrelevant and skewed facts, because Skorpion > Anomaly > Trilliax is linear, and then bosses 4-8 are non linear.
You can't take completion on 3 linear bosses and then compare that completion to one of the 5 options in a spot in the instance where you have that choice. Of course, having 5 different paths to go will affect the completion percentage. Saying it's apples to apples is just providing alternate facts.