I worked on GCP until recently. I remember celebrating (in-office) our product within GCP surpassing one million dollars of revenue per day. GCP would be fine.
How are the services provided to Alphabet subsidiaries taken into account? I’d bet that the cloud bill for YouTube alone would exceed GCP revenue numbers.
In other words, if GCP is spun out, and Google services keep using it (with realistic pricing) it’s going to have a revenue far exceeding $4bn.