GCS fuse taking 10 minutes to perform ls

You are likely hitting the ops limit in this case which is set very low by default:

If you would like to rate limit traffic to/from GCS in order to set limits on your GCS spending on behalf of gcsfuse, you can do so:

The flag --limit-ops-per-sec controls the rate at which gcsfuse will send requests to GCS. The flag --limit-bytes-per-sec controls the egress bandwidth from gcsfuse to GCS. All rate limiting is approximate, and is performed over an 8-hour window. By default, requests are limited to 5 per second. There is no limit applied to bandwidth by default.

https://github.com/GoogleCloudPlatform/gcsfuse/blob/master/README.md#rate-limiting

Consider setting --limit-ops-per-sec to a higher number, or 0 if unlimited is fine.

In /etc/fstab you use limit_ops_per_sec=0 instead.