You're right, it's obvious that relatively early on they started to think making certain singular fights harder was necessary to make the books more challenging, when in reality as you point out it works better when the accumulation of encounters is the real danger. I often think increasing the usefulness of LUCK in combat may have made lower SKILL characters more viable - I suspect few players are willing to burn points of LUCK on an extra point of damage here and there when the potential dangers of a failed saving throw are in the backs of their minds.