Bigquery threads slow down queries

Good day, hopefully this is the right place to post this.
The documentation states that

increasing the number of threads can minimize the run time of your project


We recommend setting this to 4 to start with.

dbt docs - using threads

I use dbt with bigquery and I was facing queries running in timeouts. dbt runs as Cloud Run Job and I have a service account attached. I had talks to companies IT and they suggested splitting the queries on partition column and query smaller portions. I thought: “no worries, I will keep it in parallel handled by dbt, I have threads enabled, it won’t harm my performance”
When i found a lot of queries marked as ‘Slot Contention’, I considered selecting just one (1) thread and that gave me the best performance ever…
Further considerations, I really dont know if that applies here, the company I am working for requires VPC settings.

Not sure if this is of help to anybody or it finds it way to the documentation.
Thank you