Trying to wrap my my head around SDN.

I want to take my personal lab out of the L2 / VLAN age into the current day and play around with some SDN.

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Been reading up on Cisco ACI, VXLAN BGP EVPN, Arista CVP, etc... I think i have the gist of it, but one thing i can't quite grasp. My workload is almost entirely VM based, and i plan to use Open VSwitch on my hosts. From my understanding, Open VSwitch is going to do the overlay for me, the servers will be the VTEPS for the VM's.

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At this point, whats the use of ACI and the like? If the hypervisors are doing the overlay, would i not just need a basic L2 spine / leaf setup. Maybe use VPC instead of STP in that regard? The only question comes when non OVS / VXLAN devices need access to some subset of the network. In this case you would just need a switch that can be a VTEP to handle the VLAN -> VXLAN transition for those devices?

Or a router / server could do it too i guess, but a switch seems more elegant.

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EDIT: For example, using some some cisco 9332pq's as spines, VPC to some 3132q's to get a basic leaf / spine. Then on the spines do VTEP for a few SFP+ ports to feed some downstream catalysts for a non vxlan access layer.