Thank you! I mostly just felt it out as I went, but I'd say my past experience with playing a lot of these sorts of games helped with knowing how to tune the mechanics (Vampire Survivors obviously, as well as 20 Minutes Till Dawn; and some bullet hells like Enter the Gungeon, Touhou, among others). Other than that I just have a lot of past experience with hobbyist game development in general so it's largely practice :)
In that regard, there were two main decisions I made that helped reduce lag:
- I tried to design the enemies such that they were less plentiful but a bit bulkier/more aggressive so that there was less "crowd crush" to resolve
- To account for cases where the player isn't clearing enemies fast enough, or even intentionally avoids damaging enemies to amass a bigger crowd, I made it so that any enemy who lives for longer than 60 seconds will start to run away from the player instead - and despawn once they're out of the play area. This did have a side effect of having some enemies run away and then fire at you from way outside of the camera region, which I forgot to fix haha
The TL;DR is that even without a super efficient collision method, some effective game design can go a long way to help circumvent the issue