The new system won't have an impact either. So again, why change it?
1. Because arcane systems don't benefit new players, especially when they discover that what they learned is of no real value.
2. Because it probably speeds up the game (as far as I remember only the terrain changes mentioned in this dev diary don't impact performance).
3. Because it is another thing for developers to take care of as far as programming and testing are concerned.
Point 1 is incredibly important. Many people feel that EU4 is such a superior game because of its arbitrary complexity. They could more or less reduce the game to about 20 concepts and the game play wouldn't change at all.
Time itself (as a resource)
Daily intervals (for combat, travel time, conversions, constructions)
Monthly intervals (for resources)
Modifiers (for resources of any kind and combat)
Monarch points (resource)
Cash (resource)
Envoys (ambassadors, merchants, colonists)
Relations (resource, see envoys)
Over extension (see monarch points and daily ticks)
Aggressive expansion (see relations)
Manpower (resource)
Standing army (resource, see manpower and cash)
Combat (roll dice, see modifiers)
Provinces (see resources, except monarch points)
Casus belli
Truces (see time)
Subject countries
Allies
Something like this. After actually understanding many concepts in EU4 my conclusion is: cool game, now get rid of the 30-40% crap that doesn't matter at all and only add it back when it actually does something.
I'm all for allowing modding if they remove stuff, but it's their call.