The default VPC still isn't for production. Peering isn't transitive.
Custom-mode VPCs force a deliberate IP-range decision.
Custom-mode VPC
Zero subnets by default — the production choice
Shared VPC
Host project owns the network; service projects attach
VPC Peering
Private, direct, and explicitly non-transitive
If A peers with B and B peers with C, A cannot reach C through B — a common surprise for engineers expecting general routing behavior.