I'm not sure what you're expecting. Individual creatures are tuned around the idea that their level is "worth" an equivalent PC level for a challenging Normal encounter. E.g., a party of five 5th level characters should be reasonably challenged (but ultimately win out) against a party of five 5th level monsters. That's one of the most straightforward ways we can establish a baseline of equivalency for what a creature's level means. On Hard difficulty, the party should be facing superior numbers in terms of overall levels in one of three ways a) more creatures of the same level b) the same number of creatures but some are higher level or c) fewer creatures who are mostly/all higher level. Whether a) b) or c) are used depends a great deal on the individual level and creatures that make sense there. We can't flood a map with creatures if it's cramped. We can't use a higher level companion creature if the jump in levels is too severe (e.g. Wood, Stone, and Adra Beetles all span several levels).
I can personally test things on Hard, as can Bobby and a few other folks, but most of the other devs cannot. Or rather, they wouldn't really get anywhere. If I listened to them for tuning advice, Hard wouldn't be hard at all.
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And while I have put about 400+ hours into Hitman: Blood Money and can roll through most levels with any weird goofball strategy (fiber wire every person in the level, shotgun every person in the level without ever being detected by a guard, get Silent Assassin in couple of minutes, etc.) I wouldn't want IO to base their game difficulty on my level of knowledge/familiarity. The first time the vast majority of players run through the IWD or BG games, they tend to take a lot of damage or spend a lot of time using area denial and kiting tactics.
