Does zombie evolution count towards spawns or only upgrades existing zeds?

it can get incredibly frustrating to encounter high tier monsters like shockers and brutes on just your first few hours. does slowing evolution speed stall them from spawning or just merely stall existing ones upgrading?

The way that I understand it is that evolution affects new spawns and already spawned creatures. If you change the evolution speed, it should be a blanket change.

That said, there are places that will always spawn shockers and brutes, regardless of your evolution factor. If you come across an open sewer, there will be shockers around. If you go to the prison, there will be brutes.

There’s probably no avoiding those creatures existing (short of removing them from your game) and you will quickly learn how to avoid them in the early game, barring a few bad luck encounters.

Also, and this is probably going to be a bummer to you, shockers and brutes are not high-tier enemies. They’re tougher than regular zombies, but they’re pretty basic as far as things go. Your issue is not really with monster evolution, it’s more of an issue, I think, of you still being new and not knowing how to handle those situations. Keep playing and before long you’ll be rolling your eyes at shockers as you easily avoid them or shoot them from down the block while they glow harmlessly to themselves.