A VPC is analogous to a physical network, not a subnet. Nobody uses them that way because it's not easy to grok, but you can treat a VPC as a physical network complete with your own numbering and ACL policies.
If you're doing that defense in depth on a physical network, I'm impressed by your dedication but would avoid your work for wasting resources.
it's analogous to a vlan, and it's not that much work to maintain ACLs if the vlans aren't supposed to talk to each other, which they're not, that's the whole point.
If you're doing that defense in depth on a physical network, I'm impressed by your dedication but would avoid your work for wasting resources.