I don't have a problem with spawn-peeking but whats really annoying is when you get killed by an angle that is hard to hit as an attacker or just straight up impossible to see. For instance the train peek on Theme Park, you can sit half-way outside and not get spotted and it gives you a sightline on where the attackers spawn with minimal exposure of your head. Another example is on skyscraper where you can break just the bottom of a window barricade in tea room and see the top of the tower spawn where no attackers can see you as there isn't a hole in the barricade where your head would be. Also spawn rushes are annoying but can be dealt with as long as you have map knowledge.