Bosses difficulty vs average exploration difficulty balance

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WildWombat wrote:

I also wonder why maps start at 67 rather than 71 (1 higher the harvest),

The "supposed" character progression is early act 4 -> earlier maps -> rest of act 4 -> ...
So in this context the maps starting one level higher than Dried Lake makes sense.

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WildWombat wrote:

bumping them all up would provide a slight difficultly boost and make the higher ones more rewarding experience wise for the 90+ players (why is there a hard level cap?).

How rewarding and how difficult the higher maps are is balanced independently. They (GGG) have/use some adjustment table for higher tier maps to "artificially" reduce XP and make them harder. So higher maps being "unrewarding" (for XP for high level players) is a deliberate choice by GGG.

Normal enemies need to be harder and density should be a little less (Quality over quantity), outside of that, difficulty is fine.