WASM unusably slow even for a trivial example in Brave Browser

I've created a very simple example that just adds a 2d camera and shows an fps counter. Running it as a desktop app is fine and shows 60 FPS. But when trying to run it in a browser with WASM (using wasm-server-runner), it hovers around 30 FPS for a couple seconds and then drops down to 5 FPS where it stays.

Why is this so slow? This is a trivial example that isn't really doing anything except for showing the FPS counter. Anything I can do to make it faster?

Code: https://github.com/smessmer/bevy-wasm-test

Run with:
```
cargo install wasm-server-runner
cargo run --release --target wasm32-unknown-unknown
```

Start with the linked smessmer/bevy-wasm-test reproduction and run the provided cargo command in Brave. Compare its desktop and WASM frame rates, then investigate why the trivial example drops from about 30 FPS to 5 FPS. Done means identifying the cause and a concrete fix or documented limitation.

Written by the indexing model from the issue text.