🐛 BUG: wrangler struggles to respond to a benchmarking run

### Which Cloudflare product(s) does this pertain to?

Wrangler

### What version(s) of the tool(s) are you using?

wrangler@3.72.0

### What version of Node are you using?

v20.14.0

### What operating system and version are you using?

Mac OS

### Describe the Bug

### Observed behavior
Running a simple worker with wrangler, I use node to send it 500 requests. It struggles to respond to the requests, taking too many seconds, and a bunch of them fail with 503s

### Expected behavior
It shouldn't struggle, and respond quickly.

Why is it important? If we're claiming that Workers is good for high performance scenarios, we should be able to test such scenarios locally (on much more powerful machines). This particular scenario isn't even that heavy, so it's concerning that wrangler can't support it, and is indicative of some deeper problems.

### Steps to reproduce
Full repro and instructions at https://github.com/threepointone/worker-bench-errors

### Please provide a link to a minimal reproduction

https://github.com/threepointone/worker-bench-errors

### Please provide any relevant error logs

_No response_

Start with the full reproduction and instructions in threepointone/worker-bench-errors, using wrangler@3.72.0 on Node v20.14.0 as reported. Run the 500-request benchmark and inspect where requests become slow or return 503s. Done means identifying and fixing the local Wrangler bottleneck so the benchmark responds reliably without those failures.

Written by the indexing model from the issue text.