I am a big fan of the game so before I talk about this subject I would like to be clear there are many positives in recent updates and I applaud them. However...
The changes to zombie spawns and basing it on proximity has seriously nerfed stealth players.
In A21 there has been a change of direction in the new pois to spawn zombie mobs based on player location rather than player noise. With max stealth skills and equipment it is now impossible to sneak around a poi. This is a very negative change for stealth based players.
I used to be able to sneak around level five missions with a bow and take on most of the spawns before they see or hear me, it was a very rewarding approach and the complete opposite from the big guns and break down doors and/or ladder to main loot approach. However with this change I have no option other than to use my guns a lot of the time, and the smg being the prime choice with a bow due to being in the same tree just isn't as powerful as someone who has specced into bigger guns. It doesn't feel like a stealth build is any good anymore.
To fix this I would suggest going back to the old spawning system, however make stealth harder in other ways if that is deemed as a needed balance. You could make bows harder to aim by adding sway, make arrows a lot less retrievable, or tweak the settings so that you are more detectable at the extremes such as going face to face with a zombie around a corner or breaking down environment components. This could be paired with a radius of alert rather than trigger an entire area from one noise.