I take that back. For grins I just tried logging into ESXi 6.5 with the 6.0 thick client which surprisingly worked (does not work with vcenter but this particular ESXi server is not managed by a vcenter) and there are all the resource pools. So they're still there, I created a new resource pool and dropped a VM into it, no issues.
Next I close that out and try to access the ESXi with the flash-based web client. It's when I get logged into here is where I lose visibility to the resource pools. Maybe there's a view to show the resource pools in the web client that I just haven't clicked on yet.