The lesson about "delete code to improve performance" resonates. I've been down similar paths where adding middleware/routing layers seemed like good abstractions, but they ended up being the performance bottleneck.
A few thoughts on this approach:
1. Warm pools are brilliant but expensive - how are you handling the economics? With multi-region pools, you're essentially paying for idle capacity across multiple data centers. I'm curious how you balance pool size vs. cold start probability.
2. Fly's replay mechanism is clever, but that initial bounce still adds latency. Have you considered using GeoDNS to route users to the correct regional endpoint from the start? Though I imagine the caching makes this a non-issue after the first request.
3. For the JWT approach - are you rotating these tokens per-session? Just thinking about the security implications if someone intercepts the token.
The 79ms → 14ms improvement is night and day for developer experience. Latency under 20ms feels instant to humans, so you've hit that sweet spot.