One hub, attached once per network, instead of a mesh.
A Regional virtual router — real hourly + per-GB cost, real operational simplicity.
VPC AOne attachment
Transit GatewayCentral routing
VPC B, C, D...One attachment each
100 VPCs, TGW100 attachments
vs. peering4,950 connections
AWS's own Well-Architected guidance (REL02-BP04): prefer hub-and-spoke over many-to-many mesh once you're past a couple of networks.