When a real-time bidding platform lost $240k in 12 minutes due to 400ms p99 latency spikes during peak traffic, their engineering team faced a binary choice: rewrite their Node.js 22 event loop bottlenecked pipeline in Elixir 1.18 , or scale horizontally at 3x infrastructure cost. Our 14-day benchmark across 12 real-world workloads shows Elixir 1.18 delivers 4.2x lower p99 latency for WebSocket broadcast workloads, while Node.js 22 maintains 1.8x higher throughput for single-threaded CPU-bound edge cases. Here's the unvarnished truth, backed by code and numbers.…