File access in mounted volumes extremely slow, CPU bound

Docker Desktop
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Mounting consistency options in docker-compose.yml did not help. Am I testing it in a wrong way?

Docker version 19.03.1, build 74b1e89
MacOS Mojave: 10.14.6 (18G87)

docker-compose.yml:

version: '3.7'

services:

  php:
    image: php:7.3.8-fpm
    restart: always

    volumes:

      - ./mounts/ro:/test/mounts/ro:ro
      - ./mounts/cached:/test/mounts/cached:cached
      - ./mounts/delegated:/test/mounts/delegated:delegated
      - ./mounts/consistent:/test/mounts/consistent:consistent

Then:

docker-compose up -d
docker-compose exec php sh

Next, CDing into directories mounted with different consistency configuration and running:

dd if=/dev/zero of=test.dat bs=1024 count=100000

Consistent: 102400000 bytes (102 MB, 98 MiB) copied, 36.1782 s, 2.8 MB/s
Delegated: 102400000 bytes (102 MB, 98 MiB) copied, 35.1372 s, 2.9 MB/s
Cached: 102400000 bytes (102 MB, 98 MiB) copied, 34.3295 s, 3.0 MB/s
/var/www/html (non-mounted): 102400000 bytes (102 MB, 98 MiB) copied, 0.258 s, 397 MB/s