Thanks for playing the game and for the feedback <3 Good point about hold-down for firing, we didn't think about that, and it would be an excellent QoL addition. If we keep the current pacing with the horde and a relatively large number of enemies, we will definitely add it in the next iteration.
Regarding performance, could I ask which CPU and GPU you used? We managed to do only a small optimization pass before the end of the grace period, so there is surely room for more optimizations on the GPU side. On the CPU side, it should still be relatively cheap, although there might be some oopsies on Tick. In the post-jam update, we plan to redo the entire environment and will pay more attention to the optimization side for sure o7. If the scope allows, we will also try to introduce some simple graphic settings (most likely using UE's default graphics scaling system).