Step-by-step:

1. Measure the time it takes bat to highlight examples/simple.rs without cached assets, i.e. when the assets integrated into the binary are used:

% rm -rf ~/.cache/bat
% hyperfine --export-markdown /dev/tty 'bat --color always examples/simple.rs'

2. Create cached assets that are identical to the integrated assets:

% mkdir -p ~/.cache/bat
% echo "---\nbat_version: 0.18.2" > ~/.cache/bat/metadata.yaml
% cp assets/syntaxes.bin ~/.cache/bat/syntaxes.bin
% cp assets/themes.bin ~/.cache/bat/themes.bin

3. Measure again

% hyperfine --export-markdown /dev/tty 'bat --color always examples/simple.rs'

Expected result

There is no significant difference.

Actual result

There is a significant difference.

I will soon create a PR with a proposed fix.