I think a better approach to tier lists would be to create a radar chart for each master with a few different variables. You could do something like survivability, damage potential, maneuverability, crew buffing/ synergy, and keyword strength etc. That way, rather than trying to encapsulate everything that a master means and represents into two values, you cave a bit more wiggle room. It's always going to be subjective, but it would give a bit more room for comparison to evaluate say Nekima 1 vs broodmother in terms of crew buffing or raw damage potential.